Cerebral Cortex Flashcards
Cell Types
Pyramidal cells:
Excitatory via glutamate
Granule cells:
Spiny cells excitatory
Non-spiny cells inhibitory
Cerebral Laminae
Laminated appearance due to differences in cell type, size, and density.
Neocortical Laminae
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.
Regional Laminar Variations
-
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.
Neocortex
Connectivity
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.
Neocortex
Fiber Paths
All fibers pass through centrum semiovale.
Fibers connecting cortical and subcortical regions also pass through corona radiata and internal capsule.
Association Bundles
Functional Columns
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.
Centralized
Neurotransmitters
-
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
Distal Neurotransmitter Systems
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
Lateralization
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.
Blood Supply
Epilepsy
- 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
Frontal Lobe
Areas
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
Frontal Lobe Functions
Prefrontal Cortex
Functions
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.
Prefrontal Cortex
Anatomy
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
Prefrontal Hypothesis of Consciousness
- 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
Dorsolateral Prefrontal Cortex
Lesions
Apathetic, lifeless, abulic state.
Ventromedial Prefrontal Cortex
Lesion
Impulsive, disinhibited behavior.
Prefrontal Cortex
Associated Diseases
Most common cognitive disorders associated with attention deficit:
- ADHD
- Schizophrenia
- Parkinson’s disease
- Tourette’s syndrome
- Age-related memory decline
- Dementias
- Autism
- Depression
Schizophrenia
Symptoms
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
Schizophrenia
Dopamine Hypothesis
- overactive mesolimbic pathway → D2 receptors → positive sx.
- hypoactive mesocortical pathway → D1 receptor → negative sx.
Schizophrenia
Glutamate Hypothesis
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.
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
- variations that convey emotional intent
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
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
Fontal Eye Field
Brodmann’s areas 8.
Control of voluntary saccades to contralateral side.
Two projections:
-
Indirect path:
ipsilateral superior colliculus ⟾ contralateral paramedian pontine reticular formation (PPRF) -
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.
Horizontal Saccades
Mechanism
For a saccades to the right:
- right PPRF ⟾ right abducens n. ⟾ right lateral rectus ⟾ right eye to right
- right PPRF ⟾ left oculomotor n. ⟾ left medial rectus ⟾ left eye to right
Premotor Cortex
Functions
- Preparation and initiation of voluntary movements.
- Control of proximal and trunk muscles.
- Regulation of reflexes and motor set within a limb
- More involved during learning stages
- via connections to parietal cortex
- optimal for integrating external info with a motor plan
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
-
neurons activated during planning of movements
- Neural activity depends on the entire sequence of movements
- Not linked to specific movements
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
Premotor Cortex
Lesions
- reflex imbalance
- contralateral spasticity
-
slowing of complex limb movement
- possibly due to poor facilitation of M1 neurons by lesioned premtor cortex
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.
Emotional Mirrors
Anatomy of Autism
Supplementary Motor Cortex
Characteristics
Brodmann’s areas 6 - medial portion.
Input mostly from VA thalamus.
Function:
- Planning of complex sequences of voluntary movement.
- Bilateral coordination of limbs.
- Involved internally guided actions.
Activated by:
- Mental rehearsal of complex seqeunce of movements
- During actual movements
- More activated during skilled phase
Lesion:
- Motor apraxia
- Deficit in bimanual coordination
Supplementary Motor Cortex
Activation
Activated during mental rehersal of complex sequence of movements and during the actual movement.
-
Repetitive simple finger flexion
- activates hand region of contralateral primary sensory and primary motor cortices
-
Complex sequence of finger movements
- activates contralateral supplementary motor areas & primary sensory and motor cortices
-
Imagining complex sequence of finger movements
- activates supplementary motor areas bilaterally
Primary Motor Cortex
Functions
- Execution of fractionated voluntary movements
- Fine control of distal muscles
- Body posture adjustments
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
Corticospinal Tract
Input mostly from premotor, primary motor, and primary somatosensory cortices.
Corticobulbar Tract
Input mostly from premotor and primary motor cortices.
Motor Homunculus
Somatotopic motor representation within primary motor cortex.
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.
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
- M1 neurons tuned to a preferred direction of movement
Parietal Lobe
Areas
5 functional areas:
- Primary somatosensory cortex ⟾ BA 1, 2, 3a, 3b
- Superior parietal lobule ⟾ BA 5, 7
-
Inferior parietal lobule
- Divided into 2 gyri
- Supramargial gyrus ⟾ BA 40
- Angular gyrus ⟾ BA 39
- Divided into 2 gyri
-
Posterior parietal association cortex
- Includes both inferior and superior parietal lobules ⟾ BA 5, 7, 39, 40
-
Wernicke’s area
- supramarginal gyrus & angular gyrus in parietal lobe ⟾ BA 40, 39
- caudal portion of temporal lobe ⟾ BA 22
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
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
Dorsal Columns System
Carries epicritic information to primary somatosensory cortex via VPL/VPM thalamus.
Anterolateral System
Carries protopathic information to primary somatosensory cortex via VMP/VPL thalamus.
Sensory Homunculus
Primary somatosensory cortex contains a somatotopic sensory organization.
Differs from motor homunculus:
Larger represenation for lips laterally
Presence of gentials medially
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.
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
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
Posterior Parietal Association Cortex
Characteristics
Brodmann’s areas 5, 7, 39, and 40.
Functions:
-
Non-dominant side
- more important for attentional processing
- attends to both ipsi and contralateral body/space
-
Dominant side
- attends only to contralateral side
- lesion partially compensated for by non-dominant side
Wernicke’s Area
Brodmann’s areas 22, 39, and 40.
Functions:
-
Dominant side (left)
- comprehension of language
- lesion = Wernicke’s aphasia
-
Non-dominant side (right)
-
understanding prosody in language that conveys emotional intent
- pitch
- loudness
- rate
- rhythm
- lesion = sensory aprosodia
-
understanding prosody in language that conveys emotional intent
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
Global Aphasia
Produced by lesions in both Wernicke’s and Broca’s areas.
Impaired fluency.
Impaired comprehension.
Impaired repetition.
Transcortical Motor Aphasia
Watershed region surrounding Broca’s area compromised.
Wernicke’s, Broca’s, and arcuate fasciculus intact.
Impaired fluency.
Normal comprehension.
Normal repetition.
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.
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.
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.
Temporal Lobe
Areas
Contains many structres involved in audition, language comprehension, object recognition, memory, and emotion.
- Primary auditory cortex ⟾ BA 41 and 42
- Secondary auditory cortex ⟾ BA 22 in superior temporal gyrus
- Part of Wernicke’s area ⟾ caudal portion BA 22
-
Inferior temporal cortex ⟾ BA 21, 20, 37
- includes middle and inferior temporal gyri
- Hippocampus ⟾ medial surface
- Amygdala ⟾ medial surface
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
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
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.
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
-
emotional deficits
- Dysfunction associated with many psychiatric conditions
Limbic Lobe
-
Cingulate cyrus ⟾ BA 23, 24
- emotion and attention
-
Parahippocampal and medial temporal lobe ⟾ BA 34, 28, 38
- emotion and short-term memory
-
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
- Limbic connections process through temporal lobe (e.g. olfactory)
Occipital Lobe
Areas
Involved in visual function.
- Primary visual cortex ⟾ BA 17
- Visual association cortex ⟾ BA 18 & 19
Adjacent regions involved in visual processing:
occipitotemporal region ⟾ ventral “what” stream
occipitoparietal region ⟾ dorsal “where” stream
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
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.
Secondary Visual Association Areas
Structure and Function
Brodmann’s areas 18 and 19
BA 18 ⟾ parastriate cortex
BA 19 ⟾ peristriate cortex
Functions:
- Integrates visual information.
- Gives meaning to visual stimulus by relating to past experiences and knowledge.
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
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
“What” Stream
Ventral occipitotemporal regions.
-
Neurons detect shapes, colors, and faces
- Found in occipitotemporal and inferior temporal cortices
- Bilateral lesion ⟾ achromatopsia & prosopagnosia
“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)
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
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
Lateral Cortical Lesions
Summary
Medial Cortical Lesions
Summary
Prefrontal Cortex
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.
Prefrontal Cortex
Tower of London Test
- Asked to preplan mentally a series of moves to take tower from starting to goal configuration
- 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
Internal Capsule
Connections
Subdivided into regions containing specific fiber pathways.
Rostral to caudal:
-
Anterior limb:
- Anterior nucleus ↔ cingulate cortex
- MD thalamus ↔ prefrontal cortex
- Frontopontine fibers: frontal cortex → ipsi pontine nucleus
- Genu
-
Posterior limb:
- VA & VL thalamus ↔ motor cortex
- VPL & VPM thalamus ↔ somatosensory cortex
- Corticospinal and corticobulbar fibers
-
Retrolenticular and Sublenticular limbs:
- LP thalamus & pulvinar ↔ occipital association cortex
- optic radiations → superior/inferior striate cortex
- auditory radiations
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
