Cognitive Neuroscience 4240 Exam 2

Further cortical pathways

information is extracted from perceived stimuli along two pathways (streams) that extend beyond the sensory cortex.

Dorsal Pathway

Extends along the superior parietal cortex, via the superior longitudinal fasciculus. Specialized for spatial processing (“where”).

Ventral

Extends along the inferior temporal cortex, via the inferior longitudinal fasciculus (white matter bundle). Specialized for object recognition and perception (‘what”).

Ventral Pathway: Posterior Regions

Simple stimuli are processed in posterior regions (features: light, lines, color).

Ventral Pathway: Anterior Regions

More complex stimuli are processed in the anterior regions (combinations of features, information from different modalities (auditory and visual), and general meaning (knowledge).

The Posterior-Anterior Gradient

The size of a neuron’s responsiveness to the visual field (receptive field) increases going from posterior to anterior.

The Posterior-Anterior Gradient: Simple features change…

with high spatial frequency (the units are smaller).

The Posterior-Anterior Gradient: Complex stimuli…

faces, tools, buildings, and scenes change with lower spatial frequency (they’re bigger).

The association cortex responds to…

multiple types or modalities of sensory information (auditory and visual).

Other multi-modal areas include…

the hippocampus and superior colliculus.

Multisensory Integration

The normal combination of information from different senses.

The Result of Multisensory Integration

results in a response that is greater and functionally-relevant than the sum of the individual parts.

Synesthesia

the abnormal combination of information from different senses, or sometimes different types of information within a sense.

How many types of synesthesia have been reported?

Over 60 types.

Grapheme Color Synesthesia

Perceiving letters and numbers in specific colors.

What is grapheme color synesthesia associated with?

May be associated with the development (or pre-existence) of abnormal connectivity between specialized areas (or via association areas).

Brain Stimulation

Methods that affect the function of a region (example: lesioning or enhancing), usually in a temporary manner. 

How is brain stimulation different from neuroimaging?

Can move beyond the correlational nature of neuroimaging and address the issue of the necessity of a brain region/system/network for a cognitive task. 

Transcranial Magnetic Stimulation (TMS)

1. Stimulating the brain with rapidly-changing magnetic fields, to induce weak electrical currents. 

2. By combining with MRI, it can be fairly focal. 

3. Usually involves interfering with (deactivating) a region, but sometimes enhances activity. 

Transcranial Direct Current Stimulation

1. Stimulating the brain with a constant, low current. 

2. Can increase or decrease a region’s activity (or its influence/connectivity with other regions). 

3. Usually applied while the subject is engaged in prolonged training on a cognitive task. 

4. Also being explored for neural rehabilitation (example: following a stroke). This type of device can speed up this process sometimes. 

Brain-Computer Interface

1. A system that uses neural activity to control a computer (or mechanical device: brain machine interface). 

2. Originally based on findings of motor activity that preceded actual movement (example: planning without execution). 

3. Increasingly researched and used with patients to fill gaps in function (example: from paralysis), but requires extensive training and feedback. 

Brain-Computer Interface: Feedback

When a measure (output) is looped (fed) back to influence the system or processing (input). Can be cognitive, social, neural, etc. 

Perception

1. The neurocognitive processes that allow us to represent, understand, and interpret sensory information. 

2. Influenced by our pre-existing expectations, experiences, and biases. 

3. While mostly beneficial, it can also lead us astray. 

Audition Pathway

Different frequencies of sounds stimulate hair cells in different locations of the cochlea.

Audition Pathway: Where are higher frequencies located?

Toward beginning (base).

Audition Pathway: Where are lower frequencies located?

Toward the end (apex).

First Step of Audition

Information travels from cochlear neurons to several relays (nuclei) in the brainstem (inferior colliculus). 

Second Step of Audition

Information then proceeds to the thalamus (medial geniculate nucleus) and finally to the primary auditory cortex (A1; in superior temporal gyrus).

Audition: Localization

• Where is the sound coming from? 

• Neurons originating in the brainstem can detect between-ear differences in features.

Audition (Localization): Intensity

Lateral Superior Olive (LSO).

Audition (Localization): Time

Arrival time/Phase: Medial Superior Olive (MSO).

Audition: Identification

1. What is causing the sound? 

2. As we’ve previously discussed, A1 is tonotopically organized. 

3. Different tone frequencies activate different cortical regions, roughly along an anterior (low) to posterior (high) gradient. 

4. Individual cells have broad preferences for tone. 

5. Information is aggregated across multiple cells (population vectors) to result in precise tone identification. 

Gustation Pathway

1. Food molecules (tastants) stimulate taste cells located in taste buds in the mouth. 

2. Information travels to the medulla and then on to the thalamus. 

3. The information ends up in the primary gustatory cortex, which consists of the anterior insula and frontal operculum (“lid”). 

4. Insula can be functionally segregated according to thirst/satiety and food type. 

5. Gustatory cortex projects secondarily to several areas involved in reward processing, such as orbitofrontal cortex, amygdala, and the hypothalamus. 

Olfaction Pathway

1. Olfactory receptors (over 1000 types) are located in the nasal cavity and uniquely exposed to the external world. 

2. When an odorant binds to a receptor, a signal is sent to the olfactory bulbs (ventral to orbitofrontal cortex). 

3. Information then travels to the primary olfactory (piriform) cortex: anterior parahippocampal cortex, amygdala, and the frontotemporal junction. 

4. Anosmia: smell blindness, can be an early sign of dementia.