Lecture 18: Cognitive Functions (Revamped)

Association cortex

Integrates information from multiple modalities – sensory, motor, emotional

Includes Parietal, Temporal, and Frontal

Parietal association cortex

Analyzes space, generates attention, and transmits sensory information to the motor system

“Where” pathway

→ V1 → V2 → MT

Temporal association cortex

(hippocampus) organizes declarative memory

also involved in higher order visual and auditory processing, language

“What” pathway → V1 → V2 → V4

Frontal association cortex

Governs “executive functions” → plans behavior, facilitates working memory, inhibits responses

Cortical Lamination

Humans have 3 to 6 cortical layers, depending on the area of cortex

→ Hippocampal cortex has 3-4 laminae

The circuitry of all cortical regions has common features:

→ Each cortical layer has a primary source of inputs & a primary ouput target

→ Each area has connections in the vertical axis (columnar or radial) and connections in the horizontal axis (lateral or horizontal)

→ Cells with similar functions tend to be arrayed in radially aligned groups that span all the cortical layers

→ Interneurons within specific cortical layers give rise to extensive local axons that extend horizontally in the cortex, linking functionally similar groups of cells

Cortical Layer 4

Typically rich in stellate neurons

Primary sensory cortex → receives input from the thalamus (the major sensory relay from the periphery)

Cortical Layer 5-6

Contains pyramidal neurons whose axons typically leave the cortex

Cortical Layer 2-3

Contains smaller pyramidal neurons that primarily have corticocortical connections

Thalamic connections

Inputs to association cortices come from:

• Mediodorsal thalamus → frontal association cortex

• Pulvinar → parietal association cortex

• Ventral anterior nucleus

These nuclei are not primary recipients of sensory or motor inputs → Instead, they receive inputs from other regions of cortex

Synesthesia

Perceptual phenomenon in which stimulation of one sensory or cognitive pathway leads to automatic, involuntary experiences in a second sensory or cognitive pathway

(Ex. “Tasting Colors”)

Contralateral Neglect Syndrome

Right parietal, right superior temporal, or right frontal brain damage → can all lead to difficulty attending to the left side of visual space (Contralateral)

→ right inferior parietal lobe is the most common

Inability to attend to objects, or even one’s own body, in a portion of space, despite visual acuity, somatic sensation, and motor ability remaining intact

Ideomotor apraxia

Inability to copy movements when asked to do so

Ex. an apraxic patient may have difficulty demonstrating hammering movements when asked, but can be perfectly capable of spontaneously hammering a nail.

Almost always associated with left hemisphere damage, but its symptoms are always bilateral

Constructional apraxia

Spatial organization is disordered

Patients cannot assemble a puzzle, draw a picture or copy a series of facial movements

Recognition neurons

Ventral visual pathway/object recognition (“what”) pathway

Face-specific neurons → also specific for orientation of face

Inferior temporal cortex

Wernicke’s area

Understanding of written and spoken language

Located in the posterior section of the superior temporal gyrus in the dominant cerebral hemisphere

→ (left side in ~ 97% of people)

Wernicke's aphasia (Receptive/Fluent Aphasia)

Impairment of language comprehension where speech is phonetically and grammatically normal, but meaningless

Broca’s area

Responsible for language and speech production

Broca’s aphasia (Expressive/Nonfluent aphasia)

Patients know what they want to say, they just cannot get it out

Typically able to comprehend words, and sentences with a simple syntactic structure, but are more or less unable to generate fluent speech

Prefrontal cortex

Includes the dorsolateral, medial, and orbital frontal cortex

Phineas Gage

First documented personality change due to frontal lobe damage

Activity in the orbitofrontal cortex provides inhibitory control over behavior

Frontal Lobe

Important in personality structure and behavior

→ Interfering might alter the course of disorders such as schizophrenia and other chronic psychiatric disorders

orbital prefrontal cortex lesion

• Inability to suppress distracting stimuli

• Impaired decision making

• Flattened affect

• Impaired social behavior

medial prefrontal cortex lesion

• Inability to focus attention

• Apathy, loss of attention to surroundings

Dorsolateral prefrontal cortex lesions

• Inability to sustain attention

• Lack of motivation and awareness

• Deficits in working memory

• Deficits in (motor) planning (temporal organization of behavior)

Planning Neurons

Neurons in the prefrontal cortex specifically fire to delayed response task

Maximally active during short delay period (red area) → location of the food

Same neurons have reduced activity during the motor response → short-term planning, not movement

Delayed Response Task

• Monkey watches experimenter place food in 1 or 2 wells

• Followed by a delay period (screen lowered)

• Monkey gets one chance to choose well containing food

• Bilaterally lesion prefrontal cortex → Diminished/abolished ability to locate food

Used to observe the role of planning neurons

n-back task

Subject is presented with a sequence of stimuli (letters, numbers).

→ The task consists of indicating when the current stimulus matches the one from n steps earlier in the sequence

Wisconsin Card Sorting Task

Frontal patients are unable to switch once a criterion is established → perseveration

→ Inability to use previous information to guide subsequent behavior.

Dorsolateral Prefrontal Cortex

Orbitofrontal Cortex

Neurons responded in 3 ways with regards to reward:

1. Respond to instructions (e.g. stimuli that signal reward).

2. Activation preceding reward.

3. Respond directly to reward. Magnitude of response is based on preference and animal state.

The Coke challenge

Subjective preference for Coke vs. Pepsi

→ (expressed as “Coke” selections) activates the orbitofrontal PFC

Abnormal Reward Responses

Chronic drug use (cocaine) leads to diminished basal activity in orbital PFC and anterior cingulate cortex.

In contrast, intoxication and craving result in activation of orbital PFC.

→This can be initiated by drug-associated cues.