دانشگاه صنعتی امیرکبیردانشکده مهدسی پزشکی

سمینار درس کنترل سیستمهای عصبی-عضالنی

استاد درس: آقای دکتر توحیدخواهتوسط: محمد علی احمدی پژوه

87پاییز

ناوبری در سیستمهای زیستی و مهندسی

Topics

►What is Navigation►What parts of the brain contribute in

navigation►Hippocampus►Models►Research methods►Disorders

Controller Musculoskeletal

System

SensorsSensor

Data Processing

Planning

Tasks

Navigation

RefMotorCom

Two basic methods for dealing with space

► Sensory-motor interaction with the environment: look – find target – move towards target – look requires sensory access to environment requires sensory-motor coupling

Knowledge in the world

► Representing space in memory, representing the problem, reasoning on basis of representation requires spatial memory and a representation of

the environment requires spatial inference

Knowledge in the head

Stars and other constellations

helped sailors to figure out their

position.

The red arrow is pointing to the

North Star, which is also known as

Polaris.

This is a quadrant. A sailor would see the North Star along one edge, and where the string fell would tell approximately the ship’s latitude.

A sailor could also use this astrolabe. You lined it up so the sun shone through one hole onto another, and the pointer would show your latitude.

Sailors didn’t even have good tools to tell where they were going! Look at these old charts. They were not very accurate. No wonder ships often sailed off course!

These were made over hundreds of years by sailors observing the land from the ship.

• In cognitive map of Toronto created by somebody from Toronto

Personal Communication, Created by: Meaghan Ferguson, November 02, 2004

Mapquest.com, search engine: Google.ca Accessed Novemeber 03, 2004

Insects►Bees►Ants

Visual Landmarks

►Map of local landmarks coasts, rivers, valleys, mountain ranges:

flyways? Finding nests, caches, fruiting trees:

controlled by hippocampus of the brain, which controls spatial memory and cognitive memory: also well developed in cowbirds

But, when cover homing pigeons with frosted lenses, they still find their way back to their loft

Solar Compass► Kramer’s funnel ink experiments with

starlings: can orient as long as they see the sun

► Matthews’ homing pigeons have a chronometer and understand the changing position of the sun relative to the direction of the destination to fly east at 6AM, you fly toward the sun, but

because your internal clock tells you it is noon, you know that the sun is in the south and that to fly east, you must fly 90 degrees to the left of the sun

► Light bulb experiments train birds to feed out of a northwest food cup. When

exposed to the sun, they continued to feed at this cup. When sun replaced by an immobile light bulb, shifted more and more to the left, thus compensating for the assumed change in position of the sun

Solar compass,

cont.► Clock-shifting experiments if you reset internal clocks

using artificial photoperiods to a noon-to-midnight period. When release bird at noon, it will think that it is 6AM

Stellar compass► Birds can also navigate on cloudy

days and nights► Radiotelemetry: thrushes fly 650

km on a firm compass bearing at night, meaning that they can compensate for the wind

► Planetarium experiments

Sunset cues

►Birds use polarized light from the setting sun

Geomagnetism, 1

► Provides both a compass and a map► Earth is a huge magnet: the magnetic

and true poles are offset, which means that measuring the angular difference between true and magnetic north gives you your position on the earth’s surface.

Geomagnetism,2

► Also provides compass because of the inclination of the magnetic field lines (poleward and equatorward)

► Walcott and Helmholtz coils

Reference Systems

► Need an external reference to figure out where to go.

► Critical for young birds: vagrancy use both geomagnetism

and stellar patterns planetarium experiments

with altered points of rotation

need some sort of celestial orientation

stellar cues are important at the start of migration, but then geomagnetism takes over

Integration of a Complex System► Star compass with rotation most

important during ontogeny► Magnetic field most important during

migration► Sunset cues also important► Landscape features

Factors influencing learning and use of information

► Age► Individual differences

Personality Social and cultural background Education

► Gender differences► Visual impairment► Familiarity and experience► Effort effects (e.g. travel time)

Sensory Organs

Inertial Navigation System

Inertial Navigation System

Gyroscope

►Sensors: External:

►Visual►Hearing►Vestibular►Tactile►Olfactory

Internal:►Muscle Spindle►Golgi Organs►Skin►Joint Sensor

Scene Matching

GPS

Navigation and Orientation In Biosystems

Wayfinding

Wayfinding in Normals

Guided by a cognitive map(Cognitive mapping)

Guided by specific landmark(s)(Route follow ing)

W AY F I ND I NG

Uses geometric relations among multiple landmarks

Learned associations between stimuli and responses

Destination need not be visible

Series of specific visible landmarks lead to one destination

Flexible Inflexible

Wayfinding in Normals

A. Route-based representations• Linear: Describes information that encodes

a sequential record of steps from a starting point, through landmarks, and finally to a destination

• The coupling of landmarks and instructions• Grounded in an egocentric coordinate

frame• Inflexible

Wayfinding in Normals

B. Map-like Representations• O’Keefe & Nadel, The Hippocampus as a

Cognitive Map (1978):

“Whereas a route specifies a starting point, a goal, and a particular direction of movement from the former to the latter, a map specifies none of these, either in its construction or usage. It can be used with equal facility to get from any particular place to any other. Additional flexibility derives from the freedom from specific objects and behaviors. If one path is blocked another can easily be found and followed.” (p. 87)

Wayfinding in Normals

C. Use of Different Navigational Strategies at Different Times• Different conditions can lead humans to use

different navigational strategies and environmental representations

• What are these different conditions?• The first is the kind of text description or view

given:• Given aerial or survey descriptions, subjects

tend to form map-like representations• Given more route-based descriptions, subjects

tend to form route-based representations• The second is environmental characteristics:

• Feature-poor environments lead to map-like representations

• Feature-rich environments lead to route-based representations

Spatial distortion

How accurately are spatial relations represented in the mind?

a) Distortion of distance (Berendt)b) Distortion of orientationc) Distortion of shape / configuration (Stevens

/ Coupe, Barkowsky)

11.3

a) Distortion of distance

Cognitive distance ≠ spatial distance

B. Berendt 1998

11.3.1

Jan Wiener

Cognitive Distance and

Route Selection

11.3.1.3

Experiment 1

Subjects view approaching a place, to the left is the landmark associated with that place.

11.3.1.4

Experiment 1

Schematic map of the environment, numbered circles represent places, different shades of gray represent the different regions (all places from one region carried landmarks belonging to the same category -> there

was a car-, an animal- and an art-region)11.3.1.5

Experiment 1 – example for a test route

One of the critical navigation tasks in the test phase (after exploration- and test-phase) : the black rectangle represents the

starting place, the black circles represent the target places. Subjects were instructed to visit all target places using the shortest

possible route.11.3.1.6

Results from 25 Subjects

Subjects preferred routes that crossed fewer rather than more region boundaries

Jan M. Wiener

11.3.1.7

Experiment 2

Birds-eye view of the virtual environment

11.3.1.8

Experiment 2

Subjects view approaching a place, each place (junction) carried a unique landmark that was invisible until subjects entered the

corresponding place (we call those pop-up landmarks), landmarks from one island were of the category animals, landmarks from the other

island were of the category cars.11.3.1.9

Experiment 2

Schematic map of the environment, numbered circle represent places, all places from one island carried landmarks belonging to the same category -> there was a car-, and an

animal-island

11.3.1.10

Experiment 2- Examples for test routes

Examples for the critical navigation tasks in the test phase (after exploration- and test-phase): the black rectangle represents the starting position, the black

circle represents the target place. Subjects were instructed to find the shortest possible route. Note

that there are at least two alternative optimal solutions

11.3.1.11

Experiment 2 - Results

Results: subjects preferred routes that allowed for fastest access to the region containing the

target.

11.3.1.12

Conclusion [Distance]► Environmental regions influence human route

planning behavior this suggests that regions are represented

in human spatial memory (along the lines of hierarchical theories of spatial representation)

► Route planning takes into account region-connectivity and is not based on place-connectivity alone

11.3.1.13

► Cognitive orientation: Categorization of spatial orientation In orientation memory, we ‘idealize’

perceived angles to get closer to multiples of 90°

Orientation

11.3.2

Distortion of shape / configuration

► Capacity restrictions do not allow us to represent all details

► Rather than leaving holes in our cognitive map, we represent coarse knowledge

► Shapes and configurations are simplified

► Representation requires fewer relations

N

Nevada

California

Reno

San Diego

11.3.3

THE TEMPORAL LOBE

TLFunction: Processes visual and auditory information, and integrates

them for emotion, spatial navigation and spatial and objectrecognition.

Includes all the tissue that lies below the Sylvian sulcus and anterior to theOL. Includes subcortical structures:limbic cortex, amygdala, andhippocampus.

TLSubdivisions of the TL

Within the TL:• Superior Temporal Gyrus: multimodal receiving inputs from auditory, visual and somatic regions as well as from the FC, PC and paralimbic cortex.• Middle Temporal Gyrus: (Limbic cortex). Includes the amygdala, uncus, hippocampus, subiculum, entorhinal and perirhinal cortices and the fusiform gyrus.• Inferior Temporal Gyrus: (Visual regions). Includes the fusiform gyrus, called TE.

TLConnectionsThe TL receives afferents from the sensory systems, and sends efferents to parietal, frontal, limbic system and basal ganglia.5 distinct types of cortico-cortical connections:

1. Hierarchical sensory pathway: From primary and secondary visual and auditory areas. Ventral stream. For stimulus recognition.

2. Dorsal auditory pathway: From auditory areas to PPC. For detecting spatial localization of auditory inputs.

3. Polymodal Pathway: parallel projections from the visual and auditory association areas into the STS. For stimulus categorization.

TLConnections cont…

4. Medial Temporal projection: from the visual and auditory association areas into the medial temporal or limbic. Called: perforant pathway. For long term memory.

AA perirhinal entorhinal hippocampus amygdala

5. Frontal lobe projection: from the visual and auditory association areas into the FL. For movement control and short term memory.

TLTheory of TL FunctionOn the basis of cortical anatomy 3 basic sensory functions:

1. Processing of auditory input2. Visual object recognition3. Long term storage of sensory input (memory)

The TL is a WHAT system for auditory and visual info that is going to:1. Identify2. Categorize3. Store4. Give affect

TLSymptoms of TL Damage

1. Disturbance of auditory sensation and perception2. Disorders of music perception3. Disorders of visual perception4. Disorders in the selection of visual and auditory input5. Impaired organization and categorization of sensory input6. Inability to use contextual information7. Impaired LTM8. Altered personality and affective behavior9. Altered sexual behavior

Short-term (seconds to hours) and long-term memory

The effects of cortical le-sions on maze perfor-mance

Information flow through the medial temporal lobe:

http://connection.lww.com/go/137/FSLO-988834617-678137.JPEG

Role of the hippocampus in spatial learning and memory

Anatomy of the hippocampus: connections from the entorhinalcortex and from the fornix.

Tri-synaptic pathway in the hippocampus:1. Perforant path: from the entorhinal cortex to granule cells2. Mossy fiber path: axons of granule cells synapse with CA3 cells3. Schaffer collaterals of CA3 cells synapse with CA1 cells

www.benbest.com/science/ anatmind/anatmd7.html

تولید مسیر و برنامه ریزی حرکتی

تولید سیگنال مرجع برای بخش کنترل حرکتی►

مدلهای ارائه شده برای هیپوکامپ

مدلهای مبتنی بر شبکه عصبی ►خود سازمانده

مدلهای مبتنی بر شبکه بازگشتی►مدلهای مبتنی بر شبکه رقابتی►مدلهای آشوبی►

Effects of hippocampal lesions on spatial learning:

1. In humans, lesions to the hippocampus affect only certain typesof memories; specifically declarative or episodic memories, butnot procedural memories.

2. Episodic memories: memories for facts and events; proceduralmemories: riding a bicycle, playing tennis etc.

3. Lesions to the hippocampus also cause marked deficits in spatiallearning tasks in rats.

Function: Vision: perception of form, movement and color.

OL

Separated from parietal lobe by:Parieto-occipital sulcus. Within the OL 3 landmarks:• Calcrine fissure: Div. The upper and lower halves of the visual world.• Lingual Gyrus: V2 & VP• Fusiform Gyrus: V4

THE OCCIPITAL LOBE

Subdivisions of the OL

(6+ Areas)

OL

1. V1

2. V2

3. V3

4. V3A

5. V4

6. V5

Primary VisualCortex

Secondary VisualCortex

V1 Largest area, called striate cortex. Receives the largest input from the LGN and projects to ALL other occipital regions. 1st processing level.

V2 Also projects to all other occipital areas. Segregates info from V1.

V1

V2V3 (A)V4V5

V2

V1V3 (A)V4V5

OLConnections

2 Pathways into the visual brain

OL

Eye

LGN V1V2

Dorsal (ParL)“How” or Where”

Visual Guidence of mov.

1

Ventral (TempL)“What”

Obj. perception & recog.

Tectum(Sup Colli)

Pulvinar(Thal)

Medial

Lateral2

1. Geniculo-striate system2. Tecto-pulvinar system

Connections cont…

Visual processing in humans does NOT culminate in the Secondary visual ares (V3, V4, V5) but continues within multiplevisual regions in the parietal, temporal and frontal lobes.

Beyond the Occ. L

OL

OLTheory of O.L FunctionV1 & V2 function like mailboxes: segregating info to other areas

involved in the perception of: Color/Form/Motion

V3 Dynamic form (dancing)V3A Just form

V4 Color & ShapeV5 Perception of motion

V2 Like V1 but less severeV3 Perception of form is affected

V1 If everything else intact, Ss act like if they were blindbut visual input still gets through the other areas (V2)“BlindSight”

V4 Vision in gray shadesV5 Can’t perceive objects in motion

Selective Lesions Affect specific functions

OLTheory of O.L Function Cont…5 Types of visual functions

1. Vision for action: Visual processing required to direct specific movements.

2. Action for vision: Active search of the target object. Selective attention.

3. Visual Recognition: Ventral stream infoto the temporal lobe specialized in recognition of faces “Grandmother cells”

Grandma!

OLTheory of O.L Function Cont…

5 Types of visual functions

4. Visual Space: Visual info comes form specific location in space. Objects have a location relative to an individual (egocentric),

or to one another (allocentric).

5. Visual Attention: Process of features of the visual world (otherwiseit would be too much!).

Dorsal & Ventral stream functions

OL

Milner & Goodale studies

Patient DF: Blind but dorsal streamintact, so patient shaped her handAppropriately while reaching.“Unconsciously” see locationsize and shape.

Patient VK: Ventral stream intact,Can see objects but can’t reachAccurately or shape the hand.

OL

1. Agnosias2. Monocular Blindness3. Bitemporal Blindness

Symptoms of OL Damage

6. Quadrantanopia7. Scotoma

4. Nasal Hemianopia5. Homonymous Hemianopia

1. Object Agnosiaa) Apperceptiveb) Associative

2. Other visual AgnosiasAlexiaVisual-spatial agnosia

Prosopagnosia:

1. Object Agnosiaa) Apperceptive agnosia: Can’t recognize an object although basic visual functions (color, motion etc.) are preserved. Can’t copy or match simple objects. Can see one thing at a time: Simultagnosia. Diffuse bilateral lesion in the ventral stream in OL.

b) Associative agnosia: Can’t recognize objects in spite of being to perceive them. Subjects can describe the object, know what it is for, copy it, but can’t identify it. Lesion in ventral stream in TL.

Symptoms of OL Damage Cont…

OL

OL

• Function of OL is vision, perception of form movement and color.• Three major routes: ventrally into the temporal lobe, dorsally into the parietal lobe, and a middle route going to the STS.• Ventral stream for stimulus recognition, dorsal stream for guidance of movements in space.• Some occipital regions are functionally asymmetrical: word recognition on the left and facial recognition and mental rotation on the right.

Summary:

THE PARIETAL LOBE

PL

Function: Processes and integrates somatosensory and visual infowith regard to the control of movement.

Separated from the frontal lobeBy the central fissure, from the Temporal lobe by the SylvianFissure and from the occipitalLobe by the parieto-occipitalSulcus.

PL

Within the PL:• Postcentral gyrus (B.A. 1,2,3)• Par Operculum (B.A. 43)• Superior Par Lobule (B.A. 5,7)• Supramarginal gyrus (B.A. 40)• Angular gyrus (B.A. 39)

Anterior Zone: Includes:Postcentral gyrus and Par OperculumCalled: Somatosensory cortex. ProcessesSomatic sensation and perception.Posterior Zone: Includes:Superior Par Lobule, supramarginal &angular areas. Called: Posterior ParietalCortex. Processes control of movement with somatic and visual info.

Subdivisions of the PL

PL

von Economo’s maps 3 PP areas:PE, PF, PG

Connections

1. The somatosensory cortex projects to PE, primary motor cortex, Supplementary and premotor areas. For tactile recognition, sensory info about limb position in the control of movement.

S1

PEM1SupMPreM

PLConnections cont…

2. PE output to M1 to guide movement with tactile information, inputfrom S1 (1,2,3).

3. PF output to M1 to guide movement with tactile and visual info input from S1 through PE.

4. PG output to FL. Main dorsal stream, vision for action control ofspatially guided behavior. Input from visual, somesthetic, proprioceptive,auditory, vestibular, oculomotorand cingulate.

PL

Connections cont…

5. PG output to paralimbic for memory of movements6. PG & PF output to PFC for STM of visual guided movements.7. PG output to temporal for processing the shape of objects

So, the APC processes somatic sensation and perception and the PPC integratessensory input from the somatic and visual regions for the control of movement.

PLTheory of P.L Function

There must be a spatial (internal) representation of things. There is amap or several maps that:

• Make movements to different objects• Discriminate similar objects• Make movements relative to body position• Order the movements• Attend to some objects and ignore others

Other aspects of PL function:

1. Arithmetic: Math has quasi-spatial nature, you have to manipulatenumbers in space. Left tempo-parietal.

2. Language: Also quasi-spatial demands: “tap” “pat” same lettersdifferent spatial organization

3. Understanding sequences of movement

PL

Somatosensory symptoms(anterior zone, areas 1,2,3,43)

1. Somatosensory thresholds:

2. Perceptual Disorders

3. Blind touch4. Somatosensory agnosias:

2. Simultaneous Extinction: objects can only be perceivedif presented one at a time R>L

PL

Neglect follows a RPPLx because the integrationof the spatial properties of stimuli becomes disturbed. Although stimuli are perceived, theirlocation is uncertain to the CNS= ignore it.

Posterior Parietal Symptoms(PE, PF, PG)

1. Balint’s syndrome2. Contralateral neglect3. Object recognition:4. Gerstmann syndrome5. Language deficits

7. Recall deficits8. Acopia9. Spatial Attention10. Spatial Cognition11. Attentional shift for action12. Mental imaging6. Apraxia: a. Ideomotor

b. Constructional

PL

Neuropsychological Assessment

Maze learning

Edward Tolman’s ideas of cognitive maps:an internal representation of the spatialattributes of the maze.

Cognitive map could be used to solve current and novelspatial problems

What types of experimental paradigms are used to studymechanisms underlying spatial learning/maze learning?

1. Radial arm maze2. Water maze3. Circular platform maze

Hippocampus and working memory

Radial arm maze

Disrupted by hip-pocampal lesion.

The radial arm maze:Used to test both working and reference memory

Working memory: within a trialReference memory: across trials

Tests the rats ability to optimizeit’s search for food

Experimental evidence for different spatial learning strategies:

Experiments done by Olsen and colleagues:

3 different strategies:1) remember locations based on room landmarks2) rule based strategy: choose adjacent arms3) mark visited arms with a scent

Experiment: rotate arms of the maze after the rat has visited 3 arms.

1) result: rat avoids the spatial locations of the 3 previously visited arms

Interpretation: the result supports strategy #1, but not #2 or #3

The Morris Water Maze: a spatial learning task

Rat learns to locate the positionof a submerged platform bylearning it’s position with respectto other landmarks. Rat mustencode the spatial relationshipsbetween the platform and landmarks.

Cued learning: rat associates theposition of the platform with escapefrom the water. The platform can bemoved and the rat locates it easily.

Experimental evidence supporting spatial learning:

1. Rats trained to locate position of submerged platform

2. Platform removed and rats observed for length of timespent swimming in each of 4 quadrants

3. Trained rats spent most of time swimming in quadrant where the platform was located.

Spatial learning with the circular platform maze

A task very similar to the Morris Water Maze: the rat mustfind the location of the hole that leads to a tunnel, allowingit to escape from the platform.

12.6 Hippocampal damage impairs spatial learning (A) A rat with a hippocampal lesion shows marked perseveration in a radial arm maze. Compare with the normal rat in Figure 12.1. (8) Lesions of the hippocampus or related structures impair spatial learning (black bars) while leaving cued learning (colored bars) intact. After Olton 1977.

Effects of hippocampal lesions on spatial learning:

1. Lesions to several parts of the hippocampus caused errors in spatial learning, including perseveration: visiting the samearm many times.

2. Lesions did not affect cued learning.

Hippocampal lesions affect spatial learning in the MorrisWater maze.

Lesions to the cortex, or sham lesions have no effect.Lesions do not affect cued learning.

General principles resulting from lesion studies:

Barnes compared 3 types of studies:1. Cued learning vs spatial learning2. Effects of lesions either before or after training3. Tasks affecting either working or reference memory

General features:1. If the lesion preceded training, acquisition of both working

and reference memory were impaired, cued learningwas not impaired. Therefore the lesion specificallyaffected spatial learning, not working or reference memory

2. If the lesion takes place after training, it has much less effectas the time between the training and lesion increases. Thissuggests that the hippocampus is necessary for acquisitionand storage of short term, but not longer term memories.

Cells that code for space: hippocampal place cells

Hippocampal place cells: discovered by John O’Keefe1. Firing pattern of the cell increases when animal moves to specific locations within an area.2. Firing field of the cell: spatial area within which the placecell is active.

Nadel and O’Keefe: proposed the hypothesis that the combined activityof cells within the hippocampus creates a cognitive map of the animal’senvironment. This proposal launched many investigations by many laboratories to describe and understand this phenomenon.

Firing pattern of a place cell as the animal navigatesin the environment.

What factors control the spatial preference of a place cell?

1. Different cells encode different spatial regions. 2. The size and shape of a place field can differ.3. A place field develops over time, but remains quite

constant as long as the environment does not change.4. Visual cues are important for place cell selectivity. If

visual cues are rotated, place field will rotate as well.5. If all external cues are removed, the place field

remains intact.

Firing patterns of 4 different place cells within an arena

What internal cues are used to establish and maintaina place field in the absence of external cues?

Experiments by Patricia Sharp suggest two factors:1. Vestibular inputs and visual system inputs

Animals were restrained and the floor and walls were moved with respect to the animal’s body.

1. Firing patterns of the cells were altered wheneither sets of cues were altered.

Place cells can switch their fields under different circumstances.1. Some can be switched by turning the lights on and off.2. Suggests that place cell fields can be

context dependent, fields are flexible and can bealtered by both internal and external cues.

Role of visual cues: place fields in the dark

Experimental evidence:

1. A place field established in the light will remain intact when the lights are turned off as long as the animal remains in the chamber.

2. If the animal is removed from the chamber and reintroduced in the dark,it develops a whole new place field.

3. Another twist on the same experiment: a place field is established in the light, the animal is removed andreintroduced in the dark, remapping the place field. The lights areturned on… which place field does the cell adopt?

4. In most cases the cell adopts the most recently established place field,the one established in the dark.

Place cells and memory

Experimental evidence: experiments by O’Keefe and Speakman

Paradigm: 1. Rats were trained to locate a goal arm in a four armmaze using visual cues.

2. Rats were then trained to locate the arm after a brief exposure to the cues, but cues were removed while rats werein the maze; ie they had to remember the location of the cues.

3.With cues present, place cells behaved as expected.

4. With cues absent, the cells fired when the animal made bothcorrect and incorrect choices. Why is this???

Place cells can encode additional aspects of spatial learning

Eichenbaum’s experiment:1. Rats trained to alternateright/left turns in a maze toreceive a reward.

2. Place cells that had the sameplace field showed different firingpatterns based on whether thenext turn was right or left.

3. These place fields encoded botha location on the track and thedirection of the next turn.

4. Other cells had more traditional place fields.

Spatial dreaming

1. Experiments by Wilson and McNaughton suggest that the firingpatterns of hippocampal place cells create an ensemble code thatpredicts the movements of the animal through its environment.

2. They made recordings of up to 150 cells at a time while an animalwas exploring a new environment. Over time, an ensemble code developed. If the animal was placed in a new environment, it developed a new ensemble code for the new environment, but the oldone did not dissapear.

3. Dreaming and consolidation of memories: Wilson and McNaughton recorded from animals while they were sleeping, both before and afterthey explored a new environment.

4. Cells that fired together in response to spatial location while the animalwas awake also fired together while the animal was asleep, but only afterthe establishment of the ensemble code. Thus re-living the days events indreams may help to consolidate memories.

Head direction cells:1. A second class of hippocampal neurons that encode the direction the head is facing, irrespective of where the animal is in the environment.2. Cells are located in the postsubiculum.3. Cell properties are influenced by both external and internal cues, butdo not remap the environment.4. Cells continue to fire when external cues are removed

Two types of head direction cells with different properties: PSC cells (postsubicular cortex cells) and ADN cells (anterior dorsal nucleus of the thalamus).1. PSC cells fire when the head is facing a certain direction regardless of how it got there.2. ADN cells fire when the head will be facing a direction in the future.3. Directional tuning peak of the ADN cells shifts as a function of the angular movement of the head.

A model for how ADN cells anticipate the direction of head motion.

Two types of cells play different roles in encodinghead direction.

PSC cells encode present head direction.

ADN cells encode future head direction.These cells combine information about current head direction

and angular movement of the head to predict future head direction.

The two cell types act together to compute head direction by integratingangular head motion over time.

Long term potentiation (LTP): a cellular mechanism for shortterm memory in the hippocampus.

NMDA receptors and LTP in hippocampal pyramidal cells

Does LTP play a role in spatial learning?

Injection of AP5 prior to training blocks spatial learning in the water maze.

Forgetting is associated with a decay in hippocampal LTPin both old and young rats.

Using knock-out mice to test the role of LTP and NMDAreceptors in spatial learning.

Summary of experimental evidence:CaMKII knockout mice:

1. Show normal LTP in response to high frequency stimulation, butnot to lower frequency ranges. Lower frequencies are characteristicof inputs when the animal is exploring its environment.

2.Place cells: fewer place cells were found and those were weakerand less focused on specific regions. Place fields tended to decomposeand drift over time.

3. Spatial learning as assessed with the circular platform maze. Knockouts performed less well. They were capable of using a randomsearch strategy, to a serial search, but could not do a spatial search:Ie. progress directly to the hole.

CaMKII knockout mice show a specific deficit in spatial butnot cued learning.

NMDA receptor knock-out mice

Tonegawa and colleagues developed a transgenic mouse strain witha gene deletion that codes for a subunit of the NMDA receptor.

1. LTP and other forms of plasticity are impaired in these mice.

2. Place cells: lacked spatial specificity and there was a markeddeficit in coordinated firing patterns of cells that had similar place fields

3. Spatial learning: knockout mice showed clear deficits in spatial learningbut were capable of non-spatial learning. These animals took longer to learn non-spatial tasks.

LTP and spatial learning in NMDA receptor knockout mice

The DNMS (Delayed non-match to sample) task

Working memory

Delay:Seconds to 10 min

Medial temporal (contains hippocampus) lesions and DNMS perfor-mance (working memory)

Components of the diencephalon involved in memory

- FornixMammilary body in the hypothalamusAnterior nucleus in the thalamusCingulate cortex- Lesion in the left dorsomedial thalamussevere retro and antero amne-sia

Hippocampus and working memory

Radial arm maze

Disrupted by hip-pocampal lesion.

Place cells in the hippocampus

10 min 10 min 10 min

Are place cells related to where the animal think it is?

NW

SE

No visual cues (i.e. light off)?

Place cells in the human brain?

Figure 23.16. Activity in human brain related to spatial navigation

Maguire et al. Knowing where and getting there: a human navigation network.Science. 1998 May 8;280(5365):921-4.

PET studies

Difference between the navigation and directed navigation= hip-pocampus

Caudate: may reflect move-ment planning

Hippocampus: place cells?

Similar hippocampal activity from “imagination” of navi-gation in experienced taxi drivers

Reasons for the asymmetry is not clear

Spatial map vs. Relational memory

Spatial map: hippocampal place fields organized as the locations in space, much like the retinotopy in the visual cortex.

Relational memory: “ball A is below cone B” would be one memory.

The neocortex and working memory

http://connection.lww.com/go/829/FSLO-988834631-171829.JPEG

Prefrontal cortex and working memory:

The Wisconsin card-sorting test (should figure out the current sorting category!)

See Figure 23.23

Patients with prefrontal lesions have difficulty on this task!! Prefrontal cortex involved in the working memory

Clinical Tests of Topographic Knowledge

A. Route descriptionB. Sketch-map productionC. Problems with these traditional testsD. Tests of stimulus-specific deficits in visual

memoryE. Other tests from cognitive psychology and

related fieldsF. Maze-learning tasks (e.g., Milner’s (1965)

stylus-maze task)• Problems with maze-learning tasks

G. Virtual environment tasks• Advantages and disadvantages

Egocentric d isorien ta tion

H ead ing d isorien ta tion

Landm ark agnosia

Anterograde d isorien ta tion

Topographica l D isorientation

A Taxonomy of TD

Category 1: Egocentric Disorientation• Here, topographic disorientation is

secondary to visual disorientation• These patients cannot localize seen objects

in space• Impaired on

• a wide variety of visual-spatial tasks• wayfinding tasks in both previously familiar and

novel environments• tests of route description and sketch-map

production• Intact

• visual-object recognition• Lesion site: Bilateral or unilateral (right)

posterior parietal lobe

• A more specific (and quite rare) impairment in spatial representation, involving selective damage to allocentric spatial representations

• Patients have an inability to perceive and remember the spatial relations among landmarks in the environment, and their orientation relative to those landmarks

Category 2: Heading Disorientation

• Intact• ability to recognize landmarks• representations of egocentric space

• Impaired• recall of previously learned topographical

knowledge• the acquisition of novel topographic information• ability to describe routes or draw sketch maps

• Lesion site: Posterior cingulate gyrus (usually right)

Category 2: Heading Disorientation

• An impairment of visual recognition that is selective or disproportionate for objects in the environment that usually serve as landmarks (e.g., buildings)

• Intact • object and spatial perception• ability to describe routes, layouts, and

maps• Ability to distinguish pictures of faces

from one another• spatial learning

Category 3: Landmark Agnosia

• A interesting feature: Compensatory strategies

• Lesion site: Bilateral or unilateral (right) medial aspect of the occipital lobe, including the fusiform and lingual gyri and sometimes the parahippocampal gyrus

Category 3: Landmark Agnosia

• A topographic impairment that encompasses both spatial and landmark knowledge, and is selective for the acquisition of this knowledge

• These patients show normal topographic abilities for environments that were familiar before their brain injury

• They cannot learn new environments, however

Category 4: Anterograde Disorientation

• Impairment perhaps based on a loss of recent visual memory?

• Lesion site: Parahippocampal gyrus (usually right)

• The importance of convergent data (neuropsychological, neurophysiological, and imaging; animals and humans)

Category 4: Anterograde Disorientation

Cognitive map in the Hippocampus

►The cognitive map is represented by a population of place cells

►(O’Keefe and Nadel, 1978)

Question: How is it used for navigation ?

Question: How is it used for navigation ?

How is it used for navigation?

►To know where I am

►To know where's the next to go

Synaptic modification in hippocampal neurons (CA3 recurrent connections) is necessary for the retrieval complete spatial memory in case of a lack of cues, and rapid encoding of novel behavioral sequence. (Nakazawa et al., 2002; 2003)

Synaptic modification in hippocampal neurons (CA3 recurrent connections) is necessary for the retrieval complete spatial memory in case of a lack of cues, and rapid encoding of novel behavioral sequence. (Nakazawa et al., 2002; 2003)

Transformation between different coordinates

►To transform allocentric information into egocentric information

Problem: How does the hippocampus represent a place with multiple destinations?

Problem: How does the hippocampus represent a place with multiple destinations?

Memory-Guided BehaviorMemory-Guided Behavior

Spatial Alternation TaskSpatial Alternation Task

Memory-Guided Behavior

DisambiguationDisambiguation

TransformationTransformation

DisambiguationDisambiguation

TransformationTransformation

Temporal Coding?Temporal Coding?

Theta Phase Precession

EncodingEncoding

Immediate encoding of temporal sequence (Yamaguchi, 2003)

Cognitive map formation through sequenceencoding (Wagatsuma and Yamaguchi, 2004)

Immediate encoding of temporal sequence (Yamaguchi, 2003)

Cognitive map formation through sequenceencoding (Wagatsuma and Yamaguchi, 2004)

RetrievalRetrieval

(O’Keefe and Recce, 1993; Skaggs et al., 1996) (O’Keefe and Recce, 1993; Skaggs et al., 1996)

Working Hypothesis

Theta phase coding concurrently represent current sensory input, memory retrieval and motion selection in phase of every theta cycle. A certain period of sensory input compressed into the theta cycle gives a context, enabling context-dependent memory retrieval and motion selection.

Theta phase coding concurrently represent current sensory input, memory retrieval and motion selection in phase of every theta cycle. A certain period of sensory input compressed into the theta cycle gives a context, enabling context-dependent memory retrieval and motion selection.

Neural Network Model

i) Units in every layer are described by a non-linear oscillator.

ii) Theta phase precession is generated in EC by using oscillator synchronization.

iii) Associative connections, HP-HP and HP-SUB, are modified by using asymmetric Hebb rule.

i) Units in every layer are described by a non-linear oscillator.

ii) Theta phase precession is generated in EC by using oscillator synchronization.

iii) Associative connections, HP-HP and HP-SUB, are modified by using asymmetric Hebb rule.

Sensory inputSensory input

Place (2-dimensional)

Place (2-dimensional)

Head-direction(1-dimensional)Head-direction(1-dimensional)

Place x Head-direction(3-dimensional)

Place x Head-direction(3-dimensional)

Motion selection ( Left or Right )

Motion selection ( Left or Right )

Demonstration: Theta Phase Precession

Computer SimulationsActivities of HP unitsin rearranged plane

Computer SimulationsActivities of HP unitsin rearranged plane

(Observed by Samsonovich and McNaughton,1997)

(Observed by Samsonovich and McNaughton,1997)

Experimental DataActivities of HP unitsin rearranged plane

Experimental DataActivities of HP unitsin rearranged plane

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Oscillationof HP unit:Oscillationof HP unit:

Computer Experiment: Memory-Guided Behavior (1)

What About the Hippocampus?

What About the Hippocampus?

A. Importance of this structure for navigation in rodents• Place cells in the rat hippocampus• The hippocampus as a cognitive map• The Morris water maze (MWM)

• Rats with hippocampal lesions show significant deficits on an MWM place learning task

What About the Hippocampus?

B. Difficulty translating these animal findings into humans. It may be that:

• either left or right hippocampus can support representations of topographic space in humans

• in humans, wayfinding in previously learned environments can be accomplished without hippocampal involvement

• the human hippocampus is not specialized for place learning, but for many kinds of episodic/declarative knowledge

The Computer-Generated Arena• A human analogue of the MWM• A ‘non-immersive’ desktop virtual

environment• Participants attempt to navigate

toward a specific designated place• Proximal and distal cues signaling

spatial location can be systematically varied

Travel

►the motor component of navigation►movement between 2 locations, ►setting the position (and orientation)

of the user’s viewpoint►the most basic and common VE

interaction technique used in almost any large-scale VE

Travel tasks

►Exploration travel which has no specific target build knowledge of environment

Travel tasks (cont.)

►Search naive: travel to find a target whose

position is not known primed: travel to a target whose position

is known build layout knowledge move to task location

Travel tasks (cont.)

►Maneuvering travel to position the viewpoint for a task short, precise movements

Steering metaphor

►continuous specification of direction of motion gaze-directed Pointing (the “fly” gesture) physical device (steering wheel, flight

stick)

Target-based metaphor

►discrete specification of the goal location point at object choose from list enter coordinates

Route-planning metaphor

►one-time specification of path place markers in

world move icon on map

Manipulation metaphor

►manual manipulation of viewpoint “camera in hand” fixed object manipulation

“Natural” travel metaphors

►Walking techniques►Treadmills►Bicycles►Other physical motion

VMC / Magic carpet Disney’s river raft ride Simulation of flying

Technique classification

Travel

Start to move

Stop moving

Indicate position

Indicate orientation

position

velocity

acceleration

Target specificationRoute specificationContinuousspecification

Alternate Technique classification

Travel

Direction/TargetSelection

Velocity/Accel.Selection

Conditions of Input

gaze-directedpointingphysical props

gestureslow in, slow outphysical props

start/stop buttonsautomatic start/stopconstant movement

Bowman -- Evaluation results

►steering techniques have similar performance on absolute motion tasks

►non-head-coupled steering better for relative motion

Evaluation results – 2

►“teleportation” can lead to significant disorientation

►env. complexity affects info. gathering

►travel IT and user’s strategies affect spatial orientation

Evaluation results – 3

► manipulation-based techniques efficient for relative motion

► manipulation-based techniques that do not require an object are efficient for search, but tiring

Evaluation results – 4

► Steering techniques best for naïve and primed search

► Map-based techniques not effective in unfamiliar environments, or when any precision is required

Myths

►There is one optimal travel technique for VEs.

►A “natural” technique will always be better than another technique.

►Desktop 3D, workbench, and CAVE applications should use the same travel ITs as HMD-based VEs.

Design guidelines

►Make simple travel tasks simple (target-based techniques for motion to an object, steering techniques for search).

►Provide multiple travel techniques to support different travel tasks in the same application.

More design guidelines

►Use transitional motions if overall environment context is important.

►Train users in sophisticated strategies to help them acquire survey knowledge.

►Consider integrated (“cross-task”) ITs if travel is used in the context of another task (e.g. manipulation).

Wayfinding

►Cognitive process of defining a path through an environment, using and acquiring spatial knowledge, helped by (artificial) cues

►6DOF makes wayfinding hard: human beings have different abilities to orient themselves in an environment

Wayfinding

►Observing wayfinding as a decision making process

Wayfinding tasks

►general, explorative search Search without target

►naive searchtarget position unknown

►primed searchtarget seen before (known)

►specified trajectory movementPredefined path

Cognitive Map

►During wayfinding, a person makes use of three kinds of knowledge to built up a cognitive map of the environment:· Landmark knowledge · Procedural knowledge · Survey knowledge

Reference frames

►Egocentric reference frame: position, orientation, movement of object with respect to position and orientation of the: eyes head body

Reference frames

► Exocentric reference frame: position, orientation and movement are defined in coordinates external to body object shape object orientation object motion

Travel technique effects

►Steering technique with good strategy helps spatial orientation

►A good travel technique will integrate aids to wayfinding

►Jumping between points disturbs spatial orientation

Support of spatial knowledge acquisition ►Allow a wide field of view

►Provide motion cues for judging depth and direction of movement

►Audio could enhance visual spatial perception

►Support sense of presence: it could strengthen the construction of a cognitive map

Support of spatial knowledge acquisition►Design legible environments - allow

the user to easily see the spatial organisation of an environment, enabling the establishment of a cognitive map.

· Divide a large-scale environment into parts with a distinct character

Support of spatial knowledge acquisition· Create a simple spatial organisation in

which the relations between the parts are clear

· Support the matching process between the egocentric and exocentric frames of reference by (visual) cues, including directional cues

Support of spatial knowledge acquisition►Use real-world wayfinding principles to

build up your environment►natural environment principles►urban design principles [Lynch]►architectural design principles►artificial cues

Examples of wayfinding aids

Map usage guidelines

►Provide you are here marker

►Provide grid►Choose either north-up

or forward-up map, depending on task

►Example: World-in-Miniature