41 - Cerebral Cortex Flashcards
Unimodal cortices
Somatosensory/Motor
Visual
Auditory
Association Cortex
Combines signals from primary sensory and motor modalities to create emergent psychological properties such as:
Memory
Planning
Spatial Analysis
Language & reading (Language associates arbitrary auditory, visual or tactile symbols with concrete or abstract objects and actions
Frontal Lobe Functions
Behavioral Planning Working Memory Response Inhibition Affective Processing (Assigning Value) Expressive Language
Parietal Lobe
Attention
Spatial Location
Body Image (Knowing your limbs are yours)
Transfer of sensory information to the motor system
Temporal Lobe
Declarative Memory
Emotional Processing
Receptive Language
Functions of the Frontal Association Cortex
Motor planning - The antisaccade task Speech production Working memory Suppression of stimulus-bound behavior Must be studied with complicated paradigms (beyond simple sensory or motor deficits) Delayed Response Task = Example
Functions of the Prefrontal Cortex
Working memory
Planning of behavior over long periods of tiem
Response inhibition
Complex problem solving, the Wisconsin card sort task
Expressive aspects of language
Associating value
Perseveration
Ask for a different tactic, and they can’t change it with the rules!!!!!!!
Frontal signs at the bedside
Emergence of primitive reflexes that adults supress (Grasp reflex, suck reflex, root reflex)
Perseveration - Repetition of one complicated behavior rather than changing strategy
Failure to suppress inappropriate responses to sensory stimuli (antisaccade task or blink response to a glabellar tap)
Psychiatric aspects of frontal function
Schizophrenia - Depresed frontal function by PET and fMRI criteria. Sometimes do poorly on tasks designed to examine frontal function. Sometimes their first-order relatives do poorly too!!!
Depression - Left frontal strokes correlate with higher frequency of depression than with posterior strokes.
Parietal neurons
Respond to SALIENT objects in the visual field, not all objects.
Objects can be made salient from bottom-up or top-down criteria
Respond more intensely to attended objects than to unattended objects
Bottom-Up Criteria (involuntary attention)
Big
Bright
Moving
Blood
Top-Down Criteria (voluntary attention)
Something that has been made interesting to you.
Right Parietal Lesions
Neglect left half of objects and space.
Which is worse? Right parietal lesion or left?
“Left parietal patients have more language than space in the left fields” and the right side can compensate for left spacial deficits.
Left parietal stroke patient
Spacial deficits, then recovers
Right parietal stroke patient
May never recover
Paralyze the abducens nerve
The world “jumps to the right” when you try to move your eyes left. There is feedback from motor neurons into the visual system to try and construct spatial relationships in the world
Parietal neurons
Remap their receptive fields around the time of every saccade (which is why eye movements don’t bother us)
Parietal cortex sends spatially accurate visual information to the premotor cortex, interpreting
Where objects are in space
How big they are
What is their orientation
Parietal Signs at the Bedside
Apraxia - Inability to conceptualize or mimic a movement
Constructional Apraxia - They cannot duplicate block designs, and have great difficulty copying drawings.
Optic Ataxia - Difficulty reaching to objects in space or finding them with saccades
Extinction - Neglect of a stimulus in the affected field (visual, tactile or auditory) when presented simultaneously with an equivalent stimulus in the normal field.
Anosognosia - Patients to not recognize contralateral (usually left) limb as a part of their own body
Spatial Distortion
Denial of Illness
Cancelation task - Parietal
Start on the right, stop at the midline
Temporal Lobe and Limbic Cortex
Hippocampus - Declarative Memory
Amygdala - Emotional processing and fear
Rhinal cortex - Associating motivational value to visual objects
Temporal neocortex - mostly unimodal (auditory and visual)
Remove Hippocampus and Amygdala
Can’t remember any fact for more than 45 seconds.
Can learn motor skills that require practice, but never “remembered” practice. Almost like Groundhog day if you play all the characters at once.
This is approximated in Herpes Encephalitis and Korsikoff (thiamine deficiency)
Temporal signs at the bedside
Korsakoff’s syndrome - Requires bilateral destruction of the output of the hippocampus - fornix & mammilary body
Temporal deficits are more often behavioral (Difficulty relating to others, sexual problems, emotional problems)
Damaged hippocampus often evokes seizures (auras, visual illusions, produce complex behavioral automatisms)
Dominance
The hemisphere with speech (usually the left)
Left-dominant subjects
The right hemisphere does more spatial analysis
Children who have strokes in their dominant hemisphere before the age of 2
Develop normal speech, but lose some spatial ability as judged by psychometric spatial tasks.
Interhemispheric communication
Primary sensory modalities are contralateral.
Information from one hemi-visual field or one side of the body reaches the ipsilateral cortex through the corpus callosum.
Patients with severe epilepsy can be sometimes helped by section of the corpus callosum.
Patients with Callosal Section
Entire right hemisphere is disconnected from the speech area
Stimuli in the left visual field and the left side of the body only go to the right hemisphere
Stimuli in the right visual field and the right side of the body only go to the left hemisphere
Left hemisphere doesn’t know about info in the right hemisphere
Right hemisphere
Can’t read!!!!!
Flash a word in the left hemisphere, you’ll be affected by it, but you won’t be able to read it. Flash in the right, and you can read it.
Alexia without agraphia
Lesion that wipes out left visual field and corpus callosum
All you can see is in the left visual field
That info can’t get to the speech area
Subject can’t read
Can’t name colors
Can MATCH colors
Can name scissors because there is a motor association
Can write
Can’t read what they’ve written
