Cerebral Cortex Flashcards
Cerebral Cortex (aka Neocortex)
Lobes/regions
-frontal, parietal, temporal, occipital, insular and limbic
Columnar arrangement
-specific input/output layers
-some differences in number of layers (e.g., paleocortex)
-subtle differences in appearance/thickness of layers
▪ Broadmann classification of anatomical/functional areas in cortex
Connections of the cerebral cortex
Commissural fibers
▪ cortical connection between right and left hemispheres
- corpus callosum
▪ primary pathway between hemispheres
▪ lesions = disconnection syndromes
➢ e.g., pure word blindness (alexia without agraphia)
▪ can write, but not read
▪ language areas of left cortex have no access to visual input
- anterior commissure (between right and left temporal lobes)
Connections of the cerebral cortex
Association fibers
▪ cortical connections within the same hemisphere
➢ e.g., superior longitudinal (arcuate) fasciculus connects Wernicke & Broca’s areas
▪ lesion = conduction aphasia
Functional areas
Three areas of different function
▪ as always, it is nowhere near this simple - lots of overlap
Primary areas
▪ ‘first in, last out’
- primary motor area
- primary sensory areas
▪ receive inputs from sensory thalamus
Association areas
Unimodal association areas
▪ e.g., visual or auditory association areas
Multimodal association area
▪ multiple types of stimuli represented
Occipital Lobe
Primary visual area (area 17)
Function
- receive visual input from retina
▪ retinotopy
➢ specific map of visual field
➢ large foveal representation
Lesion
- loss of specific region of visual field
Occipital Lobe
Visual association areas (area 18, 19)
Function
- beginning (continuation?) of dorsal & ventral visual processing streams
▪ ‘where” & ‘what’ pathways
➢ see visual system notes
Lesion
- visual agnosia (= ventral stream)
- prosopagnosia (= ventral stream)
- color agnosia (= ventral stream)
- alexia
Visual agnosia (= ventral stream)
▪ inability to recognize an object by sight
Prosopagnosia (= ventral stream)
▪ difficulty recognizing familiar faces (even your own)
Color agnosia (= ventral stream)
▪ inability to recognize colors
Alexia
▪ inability to ability to understand written/printed word (language)
Parietal lobe
Primary somatosensory area (area 3,1,2) (S1) in postcentral gyrus
Somatotopically organized = sensory homunculus
Function
- cutaneous and proprioceptive information
Lesion to S1
- anesthesia (hypesthesia)
▪ loss of sensation on contralateral side
➢ e.g., unable to accurately judge location or intensity of stimulus
➢ requires a fairly large lesion – much more impairment if both S1 & S2 are involved
Parietal Lobe
Somatosensory association area (area 5,7) (S2) in posterior parietal lobe
Function
- keep track of relationships between body and outside world
- multimodal cutaneous, proprioceptive, auditory, and visual inputs
▪ includes motivation, attention, and salience of stimuli
Lesion to S2
▪ many different (or combination of ) symptoms depending on location of damage
- Agnosia (“lack of knowledge”)
Agnosia
▪ loss of sensory interpretation
▪ many sub-types of agnosia
➢ damage to association area of a specific sensory input (visual, auditory,
somatosensory)
▪ loss of ability to recognize objects, persons, sounds, shapes, or smells with sensation
and memory still intact
➢ can often identify the separate parts, but not the whole
Prosopagnosia
- can identify eye, lips, etc, but not recognize face
Agraphesthesia (cutaneous kinesthesia)
- difficulty recognizing a familiar form (number/letter) traced on the area of
skin (back, palm, etc….)
Astereoagnosia (stereoanesthesia
- tactile amnesia (tactile agnosia)
- inability to judge the form of an object by touch
Non-dominant hemisphere (right parietal lobe)
▪ large role in spatial attention
➢ lesions may cause contralateral neglect (hemispatial neglect)
▪ ignore stimuli on left side
* ignore left visual field or left side of objects
* may even claim left arm is not theirs
▪ motor neglect - does not use left limbs – although motor system is intact
▪ anosagnosia - ignorance of the presence of disease
Dominant hemisphere (left parietal lobe)
▪ helps assemble information to plan for movement
* many interconnections with premotor areas
➢ lesions may cause apraxia
▪ ideomotor apraxia
* deficit in ability to plan or execute complex motor action
* can still explain how to perform it & do it unconsciously
e.g., cannot touch nose when asked (or shown), but can spontaneously scratch an itch on nose
(similar symptoms can be seen in premotor damage)
▪ right side often takes over spatial processing after left side damage
* i.e., few cases of neglect from damage to dominant hemisphere
➢ lesions in this area often affect language strongly (see Wernicke’s aphasia below
Parietal Lobe
Angular gyrus (area 39)
Function
▪ plays role in interpretation of language, mathematics and cognition
Lesion (Gerstmann’s syndrome)
▪ sensory aphasia
➢ see discussion of Wernicke’s area below
▪ dyslexia
➢ impairment or difficulty with fluency or comprehension accuracy in the ability to
read (also may impair writing, phonics)
▪ agraphia
➢ inability to write
▪ acalculia
➢ arithmetic deficits
▪ finger agnosia
➢ inability to distinguish between fingers
▪ right-left disorientation
Parietal eye fields
scanning/smooth pursuit eye movements
Parietal lobe
Supramarginal gyrus (Area 40)
Function
▪ language perception and processing
Lesion
➢ see Wernicke’s discussion below
▪ sensory aphasia
▪ sensory dysprosodia
Temporal lobe
Primary auditory area (area 41)
Function
a receives auditory information from cochlea
▪ tonotopy = frequency map
Lesion
- rarely disabling, due to strong bilateral input (anterior commissure)
- may cause deafness if both sides are damaged (e.g. coup-counter-coup injury)
Temporal Lobe
Auditory association area (area 42)
Function
combines auditory inputs
▪ analogous to S2
▪ distinguish harmony, melody, speech, noise
2 Lesion
a total destruction of one side causes little noticeable effect
▪ auditory agnosia
➢ inability to interpret the significance of sound
Wernicke’s area –Area 22 in dominant hemisphere
➢ left side in 95% of right-handed people; 60% of left-handed
▪ includes surrounding regions of parietal lobe
➢ supramarginal gyrus & angular gyrus
➢ thus, common symptoms of damage listed here
Function
▪ production and interpretation of both written and spoken language
Lesion
▪ Fluent aphasia (aka- Wernicke’s, receptive or sensory aphasia)
➢ patients use inappropriate or nonsense words
▪ because motor speech pathways are intact, patients may talk more than usual
(thus the ‘fluent’)
➢ difficulty/inability to interpret speech
Area 22 non-dominant hemisphere
Function
▪ comprehension of non-verbal components of language (prosody)
Lesion
▪ sensory dysprosodia (sensory aprosodia)
➢ difficulty of speech in interpreting the normal pitch, rhythm and variation of
stress/tone in speech “musical aspects of speech”
Frontal lobe
Primary motor area (area 4) (M1) in pre-central gyrus
Somatotopic organization referred to as motor homunculus
Function
- major skeletal muscle control site
▪ has lowest threshold to induce movement
➢ movements are specific – single joints/muscles
- primary contributor to corticospinal (and corticopontine) tracts
Lesion of area 4
- initial contralateral flaccid paralysis, that quickly becomes
- hemiparesis with (mild) spasticity
-more obvious deficits in distal limb regions and skilled movements
Frontal lobe
Pre-motor area & supplemental motor area (area 6) in precentral gyrus/sulcus and some of
superior frontal gyrus
Function
- stimulation requires more current, but induces movement in larger groups of muscles
Lesion to pre-motor area or to supplemental motor area
- very few symptoms if damage is small and limited to one of these regions
- BUT….
▪ lesions of these areas in combination with M1 damage results in serious impairment
➢ full hemiparesis with spasticity (spastic paralysis
Frontal eye field (area 8) = middle frontal gyrus
Function
- initiation, guidance of saccades
Lesion to area 8
- loss of conjugate gaze (coupled)
▪ eyes cannot move simultaneously in the same direction in order to visualize an object
▪ destructive lesion
➢ = conjugate gaze toward lesion
➢ inability to look to contralateral side
▪ irritative (stimulating) lesion (e.g., seizure activity)
➢ = conjugate gaze away from lesion
▪ inability to look toward ipsilateral side
Frontal lobe
Areas 44, 45 in inferior frontal gyrus
Function
- motor production of language
- different role if dominant or non-dominant hemisphere
Broca’s speech area in dominant hemisphere
Function
▪ motor programs for generation of language
➢ premotor for speech (also affects written language)
Lesion to Broca’s area
▪ nonfluent aphasia (aka - Broca’s aphasia; expressive aphasia)
➢ speech is halting, lack function words (e.g., articles and pronouns)
➢ language comprehension is not affected (usually)
➢ often accompanied by right side weakness of arm and/or leg
▪ dysarthria
➢ difficulty of motor control of tongue/mouth to produce speech
▪ agraphia
➢ inability to write
▪ specific to speech
➢ i.e., not involved in dysphagia
▪ difficulty with motor function of swallowing
Frontal lobe
Area 44,45 in non-dominant hemisphere
Function
▪ prosody
➢ fluctuations in pitch, tone, loudness, melody, timing, pauses, stresses, intensity,
vocal quality and accents of speech
Lesion to area 44,45 in non-dominant hemisphere
motor aprosodia
▪ disruption of expression of non-verbal elements of speech
▪ e.g., tone, rhythm, even facial expressions
Arcuate (superior longitudinal) fasciculus
▪ white matter (association) tract
▪ connects Wernicke’s area to Broca’s area
➢ parietal/temporal cortex to frontal lobe
- damage to arcuate fasciculus may result in
▪ conduction aphasia
▪ damage is often posterior to Wernicke’s area
➢ spontaneous speech largely intact
➢ comprehension almost entirely intact
➢ difficulty in speech repetition
Prefrontal area (areas 10-12)
Function
▪ executive functions
➢ planning, insight, foresight, decision making
Two major areas of the prefrontal area
Dorsolateral prefrontal cortex
➢ function
▪ working memory (short-term memory)
➢ lesion
▪ problems with planning and attention
Ventromedial prefrontal cortex
▪ includes orbitofrontal & some anterior cingulate cortex
▪ interconnected with limbic structures (esp. amygdala)
➢ function
▪ switching behaviors
Lesions to Ventromedial prefrontal cortex
(e.g., Phineas Gage & prefrontal lobotomy)
* impulsiveness, trouble suppressing emotions, poor decision making
e.g., poor bets as seen in Damasio studies
▪ perseveration - persist on single topic
▪ akinetic mutism - frontal lobe lesion
* conscious alert patient who retains ability to move/speak but fails to do so
* damaged pathways inhibit motivation/increase apathy cause passiveness to interact or respond
▪ akinesia: lack of movement
▪ mutism: lack of speech
▪ apathy: lack of interest, indifference
Memory and learning
Temporal lobe and limbic lobes involved in complex aspects of learning and memory
▪ limbic lobe is “deep” to temporal lobe
Inferior/medial temporal lobes
- significant role in creating long-term memory/learning
- transition short term to long term memory
▪ hippocampus & entorhinal cortex
Lesion to memory
amnesia
▪ loss of memory
- anterograde amnesia
▪ loss of ability to memorize new things after “injury”
▪ seen after bilateral damage to the hippocampus
- retrograde amnesia
▪ loss of ability to recall information from before damage occurred
▪ if seen, usually psychological or the result of massive & widespread damage to many
cortical areas (e.g., late-stage Alzheimer’s)
Short-term memory
▪ Working memory
➢ few seconds to minute
▪ e.g., remember the beginning of a sentence while reading the end of the sentence
➢ requires dorsolateral prefrontal cortex
Long term memory
▪ Explicit memory (declarative memory)
- episodic & semantic memory
▪ conscious and purposeful recall of previous experiences and information (dates, facts, times, places, etc…)
▪ consolidation requires intact hippocampus to preserve as long-term memory
▪ memory in distributed neural networks in cerebral cortex
Episodic memory
▪ specific recall of the events in a person’s life
▪ evidence to suggest associated with non-dominant hemisphere
Semantic memory
▪ recall of factual knowledge of historical events/people
▪ recognize people
▪ “academic” information
▪ evidence to suggest associated with dominant hemisphere
Implicit memory
➢ memory/recall of previous experiences will unconsciously influence current task
without conscious awareness
▪ e.g., amygdala
Procedural learning (motor skills)
➢ complex motor tasks; skills & habits
▪ e.g., riding a bike, tying your shoes
➢ requires cerebellum
