Chap 15 Chemical senses

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日常觀察

為何狗的嗅覺這麼好？ 為何冰的東西比較沒味道？ 吃和聞的味道如何 combine? Flavor = smell + taste

Chemical senses are

守門員- 動用情緒，回憶- 阻止不好的食物進入體內，或者遠離不好的環境

一些問題

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嗅覺（ Olfactory system ）

生存溝通Menstrual synchronyPheromones味道Anosmia

Detection threshold Yes/no procedure

- trials with odors along with “blank” trials

- This can result in bias

Forced-choice - one with odorant and one

without

- Participant indicates which smells strongest

功能 偵測

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嗅覺（ Olfactory system ）

Difference threshold 氣流影響濃度 Ofactometer

Recognition threshold knowing names helps recognition

氣味難以用語言形容

偵測

Neural codes for olfactory quality

Olfactory mucosa is located at the top of the nasal cavity.

- Odorants come in contact with the olfactory receptor neurons (ORN).

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Neural codes for olfactory quality

嗅神經 (olfactory receptor neurons, ORN)- Contains olfactory receptors

- 350 receptors (note: only 4 visual pigments)

- But, only one olfactory receptor for one ORN

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Neural codes for olfactory quality

嗅神經 (olfactory receptor neurons, ORN)- Recognition profile

( 類似三元色論中三種受器的激發組型的解釋）

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Neural codes for olfactory quality

Olfactory bulb

- ORNs of a particular type send their signals to one or two glomeruli

- How do the glomeruli respond to different odorants?

- Optical imaging

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Neural codes for olfactory quality

Olfactory bulb- Uchida 等人 (2000) 老鼠研究發現- 碳鏈結愈長，激發的區域愈偏左

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Neural codes for olfactory quality

Olfactory bulb- 嗅球反應是取決於分子與結構的特性- hardwired response? e.g. cat odor

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Higher Level Olfactory Processing

Signals from the olfactory bulb are sent to - primary olfactory (piriform) cortex in the temporal lobe and amygdala.

- Amygdala plays a role in emotional reactions to odors.

- (then to) secondary olfactory (orbitofrontal) cortex in the frontal lobe.

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Higher order olfactory processing

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Higher order olfactory processing

我們通常都同時聞到並可以分辨兩種以上的氣味

過去經驗影響嗅覺

e.g. 白酒 (Morrot et al., 2001)

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Higher order olfactory processing

de Araujo et al.People were exposed to a mixture of a sweat-like smell and a cheddar cheese flavoring.

On some trials, they saw the label “cheddar cheese,” and on others, the label “body odor.”

Pleasantness ratings were higher for the cheddar cheese trials .

fMRI scans showed activity in the orbitofrontal cortex to be associated with the pleasantness ratings.