Cerebral Cortex Flashcards
1
Q
Cell Types
A
Pyramidal cells:
Excitatory via glutamate
Granule cells:
Spiny cells excitatory
Non-spiny cells inhibitory
2
Q
Cerebral Laminae
A
Laminated appearance due to differences in cell type, size, and density.
3
Q
Neocortical Laminae
A
Pia Mater
- Molecular layer ⟾ few cells
- External granule layer
- External pyramidal layer ⟾ smaller cells
- Internal granule layer
- Internal pyramidal layer ⟾ main efferents
- Multiform layer ⟾ to thalamus etc.
4
Q
Regional Laminar Variations
A
-
Motor cortex ⟾ agranular cortex
- dominated by pyramidal and agranular laminae
-
prominent layer V
- larger cells makes it much thicker
-
Sensory cortex ⟾ granular cortex
- dominated by granule cells
- prominent layer IV
- layers referred to as supragranular (I, II, III) or infragranular (V, VI)
-
Primary visual cortex ⟾ striate cortex
-
reciprocal fibers of lamina IV very prominent
- forms distinct stripes above and below lamina
- called inner and outer bands of Baillarger
-
reciprocal fibers of lamina IV very prominent
- Association and limbic cortex also agranular.
5
Q
Neocortex
Connectivity
A
Major connections of neocortex includes:
- afferent
- efferent ⟾ primarily from lamina V
- intracortical/association fibers ⟾ communicate within hemisphere
-
commissural ⟾ across hemispheres
- to lamina I-IV via corpus callosum/anterior commissure
Cortical afferents and efferents organized within internal capsule.
6
Q
Neocortex
Fiber Paths
A
All fibers pass through centrum semiovale.
Fibers connecting cortical and subcortical regions also pass through corona radiata and internal capsule.
7
Q
Association Bundles
A
8
Q
Functional Columns
A
Cortical neurons arranged in vertical columns ⟾ functional units.
Involves processing of multiple inputs and outputs.
Very complex interconnectivity.
Depends on early stimulation for normal development.
Ex. visual cortex with orientation & ocular dominance columns.
9
Q
Centralized
Neurotransmitters
A
-
Excitatory interneurons
- mainly Glu and Asp
- found in pyramidal and spiny stellate cells
-
Inhibitory interneurons:
- mainly GABA
- found in non-spiny stellate cells
-
Neuroactive peptides:
-
modulates activity of other neurontransmitters
- CCK
- neuropeptide Y
- substance P
- somatostatin
-
modulates activity of other neurontransmitters
10
Q
Distal Neurotransmitter Systems
A
Transmitters arising from remote neurons.
Often project broadly across neocortex.
-
Serotonin
- from raphe nuclei
- terminate mainly in lamina III and IV
- may sharpen sensory processing
- role in sleep and pain
-
Norepinephrine
- from locus coeruleus
- terminate mainly in infragranular layers (V & VI)
- role in sleep
-
Acetylcholine
- from nucleus of Meynert
- role in learning and memory
- deficient in Alzheimer’s
-
Dopamine
- from mesolimbic pathway
- excessive levels in Schizophrenia
11
Q
Lateralization
A
Each cortical lobe with one or more major functions.
Each lobe with lateralization ⟾ left side controls right body.
Left cerebral hemisphere dominant in most people.
12
Q
Blood Supply
A
13
Q
Epilepsy
A
- Excessive neuronal activity in hippocampal formation or cerebral cortex
-
↑ [glutamate]
- may be toxic esp. to inhibitory interneurons
- Often see ↓ # of inhibitory interneurons in focal areas
- need GABA to supress neuron activity
- usually treat epilepsy with anticonvulsant drugs
- enhanges GABAergic inhibition
- if unresponsive can try cuting corpus callosum to limit spread of activity
-
Temporal lobe seizures mot common
- involves paroxysmal events in amygdala, hippocampus, or parahippocampus
- Seizures recur and increase in frequency/severity in most cases if untreated
14
Q
Frontal Lobe
Areas
A
5 functional areas:
- Prefrontal cortex ⟾ BA 9, 10, 11, 12, 46, and 47
- Broca’s area ⟾ BA 44 & 45
- Frontal eye field ⟾ BA 8
- Premotor & supplementary motor ⟾ BA 6
- Primary motor cortex ⟾ BA 4
15
Q
Frontal Lobe Functions
A
16
Q
Prefrontal Cortex
Functions
A
Functions:
- decision making
- judgement
-
working memory
- temporarily storing and using information required to perform complex tasks
- suppression of innappropriate responses
- ability to feel and express emotions
- personality
- empathy
- goal directed behavior
- motor functions
- sensorimotor integration
-
center for executive functions
- controls activities of other cortical areas
Neurons react to visual, auditory, somatic, olfactory, and gustatory stimuli.
May be mono, bi, or trimodal but show target specificity.
Finishes maturing relatively late in mid-twenties.
Patients with damage to prefrontal lobe unable to sustain a plan of action and meet goals.
17
Q
Prefrontal Cortex
Anatomy
A
Brodmann’s areas 9, 10, 11, 12, 46, 47.
Two main regions:
-
Dorsolateral prefrontal cortex:
- planning and working memory
-
Ventromedial prefrontal cortex:
- decision making associated with reward and punishment
- suppression of inappropriate responses & emotional reactions
18
Q
Prefrontal Hypothesis of Consciousness
A
- Working memory core process of PFC
- Conscious thought may be due to interaction between neurons for “on-line” processing of mental representations of inside and outside work
- Associated with:
- attention
- stress
- emotion
- problem solving and decision making
- thinking
19
Q
Dorsolateral Prefrontal Cortex
Lesions
A
Apathetic, lifeless, abulic state.
20
Q
Ventromedial Prefrontal Cortex
Lesion
A
Impulsive, disinhibited behavior.
21
Q
Prefrontal Cortex
Associated Diseases
A
Most common cognitive disorders associated with attention deficit:
- ADHD
- Schizophrenia
- Parkinson’s disease
- Tourette’s syndrome
- Age-related memory decline
- Dementias
- Autism
- Depression
22
Q
Schizophrenia
Symptoms
A
Schizophrenics w/ similar cognitive sx as damaged prefrontal cortex.
-
Positive symptoms:
- delusions
- hallucinations
- extreme emotions
- hyperactivity
- incoherent thoughts and speech
-
Negative symptoms:
- lack of emotion, speech, social interaction, and action
23
Q
Schizophrenia
Dopamine Hypothesis
A
- overactive mesolimbic pathway → D2 receptors → positive sx.
- hypoactive mesocortical pathway → D1 receptor → negative sx.
24
Q
Schizophrenia
Glutamate Hypothesis
A
Hypofunctional glutamate system → decreased prefrontal cortex function (hypofrontality).
Schizophrenia-like sx reproduced in healthy pepole with NDMA glutamate receptor antagonists (e.g ketamine/PCP).
Does not negate dopamine hypothesis.
Suggests ∆ in both glutamatergic and dopaminergic systems involved.
25
Broca's Area
Characteristics
**Brodmann's areas 44 and 45.**
Located in the inferior frontal gyrus.
Also called **pars opercularis** and **pars triangularis**.
* **Dominant side** ⟾ _production of written and spoken language_
* lesion ⟾ **Broca's aphasia**
* **Non-dominant side** ⟾ _prosody in language_
* variations that convey emotional intent
* pitch
* loudness
* rate
* rhythm
* lesion ⟾ **motor aprosodia**
26
Broca's Aphasia
AKA: motor aphasia, nonfluent aphasia, expressive aphasia
From damage to **dominant side of Broca's area**.
Ranges from **near muteness** to **telegraphic/agrammatic speech** (slow and effortful speech of \> 4 words).
Patient shows:
* non-fluent speech
* poor naming
* intact comprehension
* poor repetition
* writing and sign language compromised
27
Motor Aprosodia
From damage to **non-dominant Broca's area**.
**Impaired production of affective prosody and facial gestures.**
* flat monotone voice
* loss of spontaneous gesturing
* impaired ability to imitate emotional tone of a statement
* can still understand affect prosody from someone else
* may understand/want to express emotion but cannot produce it
* regions for planning/execution level of affective prosody damaged
28
Fontal Eye Field
Brodmann's areas **8**.
**Control of voluntary saccades to contralateral side.**
Two projections:
1. _Indirect path:_
**ipsilateral superior colliculus** ⟾ **contralateral paramedian pontine reticular formation** (PPRF)
2. _Direct path:_
⟾ **contralateral PPRF**
****
_Lesion_ **⟾ iability to make voluntary saccades to the contralateral side.**
Reflex saccades in response to external stimuli intact.
Becomes guided by external stimuli.
29
Horizontal Saccades
Mechanism
For a saccades to the right:
1. right PPRF ⟾ right abducens n. ⟾ right lateral rectus ⟾ right eye to right
2. right PPRF ⟾ left oculomotor n. ⟾ left medial rectus ⟾ left eye to right
30
Premotor Cortex
Functions
1. **Preparation and initiation of voluntary movements.**
2. **Control of proximal and trunk muscles.**
3. **Regulation of reflexes and motor set within a limb**
4. More involved during **learning stages**
* via connections to parietal cortex
* optimal for integrating external info with a motor plan
31
Premotor Cortex
Characteristics
**Brodmann's areas 6 - lateral portion.**
* Activated before primary motor cortex.
* Contributes **~ 30% of output to corticospinal/bulbar tracts**.
* Input mostly from **VA thalamus**
* **Modulates M1 and brainstem motor systems**
* _Contains:_
* **neurons activated during planning of movements**
* tasks relying on external cues
* guided by visual, auditory, somatosensory feedback
* **mirror neurons**
* Neural activity depends on the entire sequence of movements
* Not linked to specific movements
32
Premotor Cortex
Neurons for Planning
Brodmann's areas 6 - lateral portion.
* **neurons activated during planning of movements**
* tasks relying on external cues
* guided by visual, auditory, somatosensory feedback
* **Neural activity depends on the entire sequence of movements**
* Not linked to specific movements
* Neurons linked to a situation starts firing when cue appears, before signal to actually move
33
Premotor Cortex
Lesions
* **reflex imbalance**
* **contralateral spasticity**
* **slowing of complex limb movement**
* possibly due to poor facilitation of M1 neurons by lesioned premtor cortex
34
Mirror Neurons
**Found in premotor cortex, insula, and cingulate gyrus.**
Activated while **doing an action** and while **watching someone perform the same action**.
Mirror circuits gives observer an experiential understanding of observed action ⟾ **imitation**.
**Carries intention understanding information.**
Ex. grabbing peanut for eating but not by grabbing peanut to put in a bag.
Causes activation of frontal, temporal, and parietal areas in humans.
Underly empathy, learning by observing, and social interaction.
35
Emotional Mirrors
36
Anatomy of Autism
37
Supplementary Motor Cortex
Characteristics
**Brodmann's areas 6 - medial portion.**
**Input mostly from VA thalamus.**
_Function:_
1. **Planning of complex sequences of voluntary movement.**
2. **Bilateral coordination of limbs.**
3. Involved **internally guided actions.**
_Activated by:_
1. **Mental rehearsal** of complex seqeunce of movements
2. During **actual movements**
3. More activated during **skilled phase**
_Lesion:_
1. **Motor apraxia**
2. **Deficit in bimanual coordination**
38
Supplementary Motor Cortex
Activation
Activated during mental rehersal of complex sequence of movements and during the actual movement.
1. **Repetitive simple finger flexion**
* activates hand region of _contralateral primary sensory and primary motor cortices_
2. **Complex sequence of finger movements**
* activates _contralateral supplementary motor_ areas & _primary sensory and motor cortices_
3. **Imagining complex sequence of finger movements**
* activates _supplementary motor areas bilaterally_
39
Primary Motor Cortex
Functions
1. Execution of fractionated voluntary movements
2. Fine control of distal muscles
3. Body posture adjustments
40
Primary Motor Cortex
Characteristics
**Brodmann's areas 4.**
**Precentral gyrus.**
* **Agranular**
* Known as **M1**
* Contains:
* giant _pyramidal neurons_ ⟾ **Betz's cells**
* neurons encoding **force, velocity, and direction**
* Contributes **~50% to corticospinal and corticobulbar tracts**
* _Input_ mostly from **VL thalamus**
* **Somatotopic motor representation** (homunculus)
* Site of jacksonian seizures
* Used in brain-machine interface
41
Corticospinal Tract
Input mostly from premotor, primary motor, and primary somatosensory cortices.
42
Corticobulbar Tract
Input mostly from premotor and primary motor cortices.
43
Motor Homunculus
Somatotopic motor representation within primary motor cortex.
44
Jacksonian Seizures
**Focal motor seizures.**
**Unilateral clonic movements starting in one muscle group and spreading systematically to adjacent groups.**
Reflects movement of epileptic activity through motor cortex.
45
M1 neurons
**Neurons within primary motor cortex.**
* **Firing rate** ⟾ _amount of force to a muscle_
* Some encode **rate of change of force** ⟾ _control speed of movement_
* **Direction of movement encoded by populations of neurons**
* M1 neurons **tuned to a preferred direction of movement**
* represented as a vector
* Resultant vector for population of M1 neurons matches actual direction of movement
46
Primary Motor Cortex
Lesion
* **Small lesion in limb area not involving trunk area**
* **contralateral weakness or flacid paresis** of fine voluntary movements in affected parts
* **Babinski sign**
* **Large lesion including trunk area**
* _sx above and_ **contralateral spasticity**
* because **only trunk area of M1** _influences_ descending **medullary and pontine reticulospinal tracts**
47
Parietal Lobe
Functions
* Primary somatosensory
* Spatial location and organization
* Guidance of reaching, motion detection
* Understanding speech and its emotional content
48
Parietal Lobe
Areas
5 functional areas:
1. **Primary somatosensory cortex** ⟾ BA 1, 2, 3a, 3b
2. **Superior parietal lobule** ⟾ BA 5, 7
3. **Inferior parietal lobule**
* Divided into 2 gyri
* **Supramargial gyrus** ⟾ BA 40
* **Angular gyrus** ⟾ BA 39
4. **Posterior parietal association cortex**
* Includes both inferior and superior parietal lobules ⟾ BA 5, 7, 39, 40
5. **Wernicke's area**
* supramarginal gyrus & angular gyrus in parietal lobe ⟾ BA 40, 39
* caudal portion of temporal lobe ⟾ BA 22
49
Primary Somatosensory Cortex
Location & Function
**Brodmann's areas 3a, 3b, 1, 2.**
**Post-central gyrus.**
**Functions in the initial processing of:**
proprioception
pain
temperature
fine touch sensation
50
Primary Somatosensory Cortex
Characteristics
**Brodmann's areas 3a, 3b, 1, 2.**
* **Granular**
* Also known as **S1**
* _Major inputs:_
* **dorsal column system**
* **anterolateral system**
* Relayed from **VPL and VPM thalamus**
* **Projects caudally to associative/integrative areas**
* Brodmann's areas 5, 7, and SII
* Contributes to **corticospinal tracts**
* Contains **somatotopic sensory homunculus**
* Shows **regional differences in signal processing**
* neurons w/ similar response properties grouped into **functionally distinct columns**
51
Dorsal Columns System
Carries epicritic information to primary somatosensory cortex via VPL/VPM thalamus.
52
Anterolateral System
Carries protopathic information to primary somatosensory cortex via VMP/VPL thalamus.
53
Sensory Homunculus
**Primary somatosensory cortex contains a somatotopic sensory organization.**
_Differs from motor homunculus:_
Larger represenation for lips laterally
Presence of gentials medially
54
Primary Somatosensory Cortex
Regional Organziation
_Most thalamic inputs_ **terminates in BA 3a and 3b**.
_Some reach directly_ to **BA 1 and 2**.
Each area has a **separate somatotopic map**.
**Different modalities** tend to **dominate each area**:
* **3a**: proprioceptors
* **3b**: cutaneous mechanoceptors
* **1:** mainly cutaneous mechanoreceptors, larger receptor fields
* **2**: convergent inputs from cutaneous mechanoceptors and proprioceptors
As info projects from 3a & 3b ⟾ 1 & 2, **convergence and crossmodality processing occurs**.
**Tactile and proproceptive info integrated in relation to body map.**
* **BA 1** ⟾ provides info about **object tecture**
* **BA 2** ⟾ provides info about **size and shape**
**Info relayed to BA 5, 7, and SII for more integration.**
55
Primary Somatosensory Cortex
Lesion
**_Contralateral:_**
* **Hemianesthesia** ⟾ loss of sensation
* **Asterognosia** ⟾ inability to identify an object by active touch only
* **Agraphesthesia** ⟾ inability to recognize letters or numbers drawn on skin by touch only
56
Superior Parietal Lobule
Characteristics
**Brodmann's areas 5 & 7.**
**Receives somatosensory, vestibular, visual, and auditory information.**
_Functions:_
* **integrates somatosensation with visual**
* provides **3D map of space in relation to body parts**
* involved in **locating objects in space in relation to self**
* info to _premotor, supplementary motor, and primary motor cortices_ for **targeted movements**
57
Superior Parietal Lobule
Lesion
_Results in deficits of:_
1. **Spatial processing**
* poor visuomotor guidance of hands, fingers, eyes, limbs, and head
* hard time catching a ball
2. **Tactile recognition**
3. **Knowing limb position**
4. **Directing movement in space**
5. **Distinguishing left from right**
58
Inferior Parietal Lobule
Characteristics
Brodmann's areas 39 and 40.
* _Supramarginal gyrus and angular gyrus_ forms **multimodal associative area**.
* Receives **auditory, visual, vestibular, and somatosensory inputs**.
* Acts as **integrative center** between _sensory modalities and speech areas_.
* _Functions within_ **dominant hemisphere**:
* **language**
* **mathematical operations**
* **space and body image**
59
Inferior Parietal Lobule
Lesion
1. **Ideomotor apraxia** ⟾ inability to use an object properly
2. **Ideational apraxia** ⟾ inability to formulate/execute a complex multistep task
3. **Constructional apraxia** ⟾ inability to put things together to form a meaningful whole
4. **Gertsmann's syndrome** (lesion to only 39 & 40)
5. **Balint's syndrome** (from a complete b/l lesion)
60
Gertmann's Syndrome
Caused by **inferior parietal lobule lesion** isolated to **dominant side**.
* **Left-right confusion**
* **Finger agnosia** ⟾ unable to recognize or name fingers
* **Agraphia** ⟾ inability to write text patient originated
* still able to copy text
* **Acalculia** ⟾ inability to understand and operate with numbers
61
Balint's Syndrome
Caused by bilateral lesion of interior parietal lobule.
* **Optic ataxia** ⟾ lack of hand/eye coordination
* **Oculomotor apraxia** ⟾ inability to voluntarily move eyes to a new location
* **Simultanagnosia** ⟾ inability to perceive more than one object at a time
62
Posterior Parietal Association Cortex
Characteristics
**Brodmann's areas 5, 7, 39, and 40.**
_Functions:_
1. **Non-dominant side**
* **more important for attentional processing**
* attends to **both ipsi and contralateral body/space**
2. **Dominant side**
* attends **only to contralateral side**
* lesion partially compensated for by non-dominant side
63
Posterior Parietal Association Cortex
## Footnote
**Unilateral Lesion to Non-dominant Side**
**Lesion affecting non-dominant (right) side:**
* **contralateral neglect of left-side**
* pays no attention to stimuli presented on left side of body
* difficulty reaching for objects, writing, drawing, or dressing on left side
* **constructional apraxia** ⟾ draws or copies figures neglecting the left half
* **asomatognosia** ⟾ ignores parts of body on left
* **anosognosia** ⟾ unaware something is wrong
Patient tested for sensory, motor-intentional, and conceptual neglect.
64
Posterior Parietal Association Cortex
## Footnote
**Unilateral Lesion to Dominant Side**
**Lesion affecting dominant (left) side:**
* **mild or undetectable contralateral neglect (right-side)**
* _deficits in:_
* spatial processing
* visuomotor guidance
* tactile recognition
* knowing of limb position
* constructional apraxia
* astereognosis
* _Gertsmann's syndrome_
* agraphia
* acalculia
* finger agnosia
* left/right confusion
65
Wernicke's Area
**Brodmann's areas 22, 39, and 40.**
Functions:
1. **Dominant side (left)**
* **comprehension of language**
* lesion = **Wernicke's aphasia**
2. **Non-dominant side (right)**
* **understanding** **prosody in language** that conveys emotional intent
* pitch
* loudness
* rate
* rhythm
* lesion = **sensory aprosodia**
66
Wernicke's Aphasia
a.k.a. sensory aphasia, fluent aphasia, receptive aphasia
**Caused by lesion to dominant side of Wernicke's area.**
* poor comprehension
* poor repetition
* paraphasic errors with naming
* fluent speech
* inability to understand writting language
67
Sensory Aprosodia
Caused by lesion to **non-dominant side of Wernicke's area**.
* **unable to decipher prosody in language**
* **cannot understand the affective tone** of spoken language
* inability to understand mood/emotion of gestures or facial expressions
* prosodic repetition impaired
68
Language Processing
**Most with left-hemisphere dominant control of language.**
Transection of corpus callosum ⟾ "split-brain" patients:
could not verbally express information only available to right hemisphere
non-verbal conmmunication intact
69
Global Aphasia
**Produced by lesions in both Wernicke's and Broca's areas.**
Impaired fluency.
Impaired comprehension.
Impaired repetition.
70
Transcortical Motor Aphasia
**Watershed region surrounding Broca's area compromised.**
Wernicke's, Broca's, and arcuate fasciculus intact.
Impaired fluency.
Normal comprehension.
Normal repetition.
71
Transcortical Sensory Aphasia
**Watershed region surrounding Wernicke's area compromised.**
Wernicke's, Broca's, and arcuate fasciculus intact.
Fluent but paraphasic speech.
Impaired comprehension.
Normal repetition.
72
Mixed Transcortical Aphasia
**Watershed area surrouding Wernicke's and Broca's areas compromised.**
Wernicke's, Broca's, and arcuate fasciculus intact.
Impaired fluency.
Impaired comprehension.
Normal repetition.
73
Conduction Aphasia
**Produced by lesions of arcuate fasciculus and supramarginal gyrus.**
Normal fluency with paraphasic errors, long pauses, and difficulty reading aloud.
Normal comprehension.
Impaired repetition.
74
Temporal Lobe
Areas
Contains many structres involved in audition, language comprehension, object recognition, memory, and emotion.
1. **Primary auditory cortex** ⟾ BA 41 and 42
2. **Secondary auditory cortex** ⟾ BA 22 in superior temporal gyrus
3. **Part of Wernicke's area** ⟾ caudal portion BA 22
4. **Inferior temporal cortex** ⟾ BA 21, 20, 37
* includes middle and inferior temporal gyri
5. **Hippocampus** ⟾ medial surface
6. **Amygdala** ⟾ medial surface
75
Klüver Bucy
Syndrome
**Caused by bilateral temporal lobe lesions.**
* **Memory disorders**
* due to lesion of hippocampus and temporal association cortex
* **Emotional deficits**
* due to lesion of amygdala
* **placidity** ⟾ diminished fear response and emotional affect
* **Hypersexuality** ⟾ sexual behavior directed towards unusual or innappropriate objects
* due to loss of descending cortical control over hypothalamus
* **Hyperorality** ⟾ compulsion to examine objects by mouth
* **Visual agnosia** (psychic blindness) ⟾ inability to recognize objects and faces
* due to damage of "what" pathway in inferior temporal cortex
* **Bulimia**
* **Distractibility** (hypermetamorphosis) ⟾ reaction to everything
76
Primary Auditory Cortex
Structure & Function
**Brodmann's areas 41 and 42.**
Also known as **transverse gyrus of Heschl**.
* **Processing of acoustic information**
* Granular
* Within posterior half of superior temporal gyrus
* **Input from medial geniculate nucleus (MGN) of thalamus**
* Contains **tonotopic map**
* high frequencies caudal
* low frequencies rostral
* neurons with similar response grouped into **vertical columns**
* Sound further processed in **secondary auditory areas**
* within superior and middle temporal gyrus ⟾ BA 21 and 22
* for complex sounds
* for cross-modality integration
77
Primary Auditory Cortex
Lesions
**Brodmann's areas 41 and 42.**
* **unilateral** ⟾ no substantial hearing loss
* **bilateral** ⟾ **cortical deafness**
* **lesions including associative areas**
* **auditory agnosia** ⟾ inability to recognize verbal or non-verbal sounds or both
* **amusia** ⟾ inability to recognize music
78
Inferior Temporal Cortex
Structure and Function
**Brodmann's areas 20 and 37.**
* _Function:_
* Associated with **ventral stream of visual processing**
* **Specialized in faces, objects, and color recognition**
* Forms **occipitotemporal ventral pathway**
* Starts in primary visual cortex
* Travels through inferior temporal cortex
* **Contains neurons activated by specific complex objects** ⟾ hands, faces, objects, colors
79
Populations Coding
Neurons differently responsive to various features of faces and objects work in concert to enable recognition of complex sensory stimuli.
80
Inferior Temporal Cortex
Lesion
_Observed following **bilateral** lesion:_
**Visual agnosia** ⟾ inability to recognize familiar objects.
**Prosopagnosia** ⟾ inability to recognize familiar faces
**Achromatopsia** ⟾ inability to perceive colors
81
Hippocampus
Major role in **consolidation of declarative memory** and **spatial memory**.
_Lesion_ ⟾ **anterograde amnesia** & **deficit in spatial memory**.
_Alcohol and thiamine deficiency_ can damage hippocampus ⟾ **Karsakoff's syndrome**.
82
Amygdala
* _Functions:_
* **attaching emotional significance** to incoming stimuli
* formation and storage of **implicit memory**
* initiating **"freeze, fight, or flight"** in response to potential threats
* _Lesion:_
* **emotional deficits**
* fearless
* decreased affect
* docility
* **inability to perceive fear in other's facial expressions**
* **interferes with fear conditioning**
* Dysfunction associated with many psychiatric conditions
83
Limbic Lobe
1. **Cingulate cyrus** ⟾ BA 23, 24
* emotion and attention
2. **Parahippocampal and medial temporal lobe** ⟾ BA 34, 28, 38
* emotion and short-term memory
3. **Orbitofrontal cortex**
* part of limbic system but not part of limbic lobe
* **ventromedial area of prefrontal cortex**
* non-dominant side → negative emotion
* dominant side → happiness
4. Limbic connections process through temporal lobe (e.g. olfactory)
84
Occipital Lobe
Areas
Involved in visual function.
1. **Primary visual cortex** ⟾ BA 17
2. **Visual association cortex** ⟾ BA 18 & 19
_Adjacent regions involved in visual processing:_
occipitotemporal region ⟾ **ventral "what" stream**
occipitoparietal region ⟾ **dorsal "where" stream**
85
Primary Visual Cortex
Structure and Function
**Brodmann's areas 17.**
Functions in **initial processing of retinal inputs.**
* Granular
* Also known as **striate cortex**
* Found within **calcarine sulcus**
* _Input from_ **lateral geniculate nucleus (LGN) of thalamus**
* _Projects to_ **associative/integrative areas**
* BA 18 & 19
* What/Where regions
* Organized into **ocular dominant** and **direction selective vertical columns**
* _Contains:_
* simple, complex, and hypercomplex cells
* neurons processing **binocular disparity**
* **blob processing color information**
86
Primary Visual Cortex
Lesion
**Macula sparing may be present.**
**Unilateral lesion of visual cortex** ⟾ contralateral homonymous hemianopia.
**Unilateral lesion of inferior bank of calcarine sulcus** ⟾ contralateral homonymous superior quadrantanopia.
**Unilateral lesion of superior bank of calcarine sulcus** ⟾ contralateral homonymous inferior quadrantanopia.
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Secondary Visual Association Areas
Structure and Function
_Brodmann's areas 18 and 19_
BA 18 ⟾ parastriate cortex
BA 19 ⟾ peristriate cortex
_Functions:_
1. **Integrates visual information.**
2. **Gives meaning to visual stimulus by relating to past experiences and knowledge.**
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Parastriate Cortex
_Brodmann's area **18**_
* **Part of the secondary visual association cortex**
* **Neurons similar to primary visual cortex**
* direction selectivity
* binocular disparity
* color sensitivity
* **Has more integrative properties**
* ****analysis of illusory contours
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Peristriate Cortex
**Brodmann's area 19.**
* Part of the secondary visual association cortex
* **Dorsal region:**
* Contains **motion sensitive neurons**
* Projects to **parietal "where" area**
* **Ventral region:**
* Specialized for **object recognition**
* Projects to **inferior temporal "what" area**
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Secondary Visual Association Areas
Lesion
**Visual agnosia** ⟾ can see visual stimuli but cannot associate them with any meaning or identify their function.
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"What" Stream
Ventral **occipitotemporal** regions.
* **Neurons detect shapes, colors, and faces**
* Found in occipitotemporal and inferior temporal cortices
* _Bilateral lesion_ ⟾ **achromatopsia** & **prosopagnosia**
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"Where" Stream
Dorsal **occipitoparietal** regions.
* Funtions in **motion and position processing**
* Located at junction of parietal, temporal, and occipital cortices
* Bilateral lesion ⟾ **motion blindness** (cerebral akinetopsia)
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Occipital Lobe
Lesion
**Lesion of left (dominant) occipital cortex** ⟾ **right homonymous hemianopia**.
* left visual hemifield intact
* can read and understand language
* _visual information from right visual cortex_ **crosses** to left via **splenium of corpus callosum**
* reaches Wernicke's area on left (dominant) side
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Alexia
Inability to read.
Caused by PCA lesion of occipital lobe in dominant hemisphere.
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Alexia without Agraphia
Results from lesion to **left (dominant) visual cortex** and **splenium of corpus callosum**.
* **Left visual hemifield intact**
* **Info from right visual cortex cannot cross**
* Cannot reach left Wernicke's area
* **Patiant cannot read but can still write**
* cannot check if writing makes any sense
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Lateral Cortical Lesions
Summary
97
Medial Cortical Lesions
Summary
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Fronto-Temporal Dementia
Other than Alzheimer's, one of the most common types of dementia.
Sx include behavioral changes associated with damage to Brodmann's areas 9, 10, 11, and 46.
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Prefrontal Cortex
Dysfunction
See problems with working memory, flexiblity, planning, problem solving, and judgement.
* **Perseveration** ⟾ difficulties in making behavioral shifts in attention, movement, and attitude.
* **Working memory deficits**
* difficulty in monitoring and manipulation of info in short term memory
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Prefrontal Cortex
## Footnote
**Abstraction and Judgement Assessment**
1. **Interpret proverbs** ⟾ "Every path has its puddle"
2. **Explain how conceptually linked words are similar** ⟾ pants and hat
3. **Plan and structures sequential set of activities** ⟾ how to bake a cake?
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Prefrontal Cortex
Perseveration, Attention, and Memory Assesments
1. **Digit span test**
* how many digits held transiently in memory
* should be \> 5
2. **Written alternating sequencing task**
* draw pattern of alternating triangles and squares
3. **Luria manual sequencing task**
* repeat sequence as quickly as possible
* tap leg with fist, open palm, and side of open hand
4. **Auditory Go-No-Go test**
* moves finger in response to one tap
* stay still in response to two taps
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Prefrontal Cortex
## Footnote
**Wisconsin Card Sorting Task**
1. Sort cards according to a simple rule
1. number, color, shape
2. Patient tries to guess rule and receives feedback
3. Once pt guesses right, rule changes
4. Pt with prefrontal damage perseverate continuing with first rule
* commits repeated errors they are aware of and can report
* cannot use to update behavior
* keeps trying to go by first rule
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Prefrontal Cortex
## Footnote
**Stroop color and word test**
Task to inhibit a habitual response for an unusual/new requirement.
Asked to read aloud as fast as possible the color of each word, not the word itself.
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Prefrontal Cortex
Tower of London Test
1. Asked to preplan mentally a series of moves to take tower from starting to goal configuration
2. Then has to execute moves one by one
* Prefrontal cortex lesion ⟾ working memory deficit
* cannot maintain and compare internally info about different steps
* cannnot monitor and manipulate info in short term memory
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Internal Capsule
Connections
Subdivided into regions containing specific fiber pathways.
Rostral to caudal:
1. **Anterior limb:**
* Anterior nucleus ↔ cingulate cortex
* MD thalamus ↔ prefrontal cortex
* Frontopontine fibers: frontal cortex → ipsi pontine nucleus
2. **Genu**
3. **Posterior limb:**
* VA & VL thalamus ↔ motor cortex
* VPL & VPM thalamus ↔ somatosensory cortex
* Corticospinal and corticobulbar fibers
4. **Retrolenticular and Sublenticular limbs:**
* LP thalamus & pulvinar ↔ occipital association cortex
* optic radiations → superior/inferior striate cortex
* auditory radiations
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Internal Capsule
Blood Supply
_MCA ⟾ **lenticulostriate arteries**:_
most of anterior and posterior limbs
genu
_Internal carotid ⟾ **anterior choroidal artery**:_
inferior and posterior regions
most of retrolenticular and sublenticular areas
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Development of Language
* **Critical periods for learning speech and language**
* Children born with severe hearing loss can possibly learn to speak "normally" if amplifier used for **auditory exposure to speech before 2 y/o**
* **Learning foreign or second language** without an "accent" must be **before 10 y/o**
* Injury to dominant hemisphere before 10 y/o can result in some **speech development in non-dominant hemisphere**
