Cerebral Cortex: Organization, Connections, and Function Flashcards
How are the three types of cortex defined? What are they?
Number of cell layers:
- Archicortex - 3 layers
- Paleocortex - 3-5 layers
- Neocortex - 6 layers (majority of cortex)
What is at the surface of the cortex in general? What is found superior and deep to this?
Layers of gray matter
Superiorly (Towards the outside) = pia mater
Deep (towards the inside) = white matter of cortex
What are pyramidal cells? What layers are they found in? Where do they project to?
Cone-shaped / pyramid shaped cell bodies with apical dendrites projecting to pia, axons projecting to white matter and entering cortical / subcortical sites.
Seen in layers 3 (small), 5 (large), and 6
What are stellate (granular) cells? What is their function and where do they project?
They are called stellate for their rounded cell bodies and radiating dendrites. They are often intrinsic and project between layers of the cortex, found in layers 2 and 4.
What are fusiform cells? Where are they found?
Spindle-shaped cells, found in outmost + innermost layers (1 + 6)
How were Brodmann’s areas determined?
Via positron emission tomography (PET) while people were doing certain tasks
What are the three major types of afferent connections to the Neocortex?
- Corticocortical
- Thalamocortical
- Subcortical
What are the corticocortical inputs to the neocortex and where do they end?
Ipsilateral - association fibers
Contralateral - commissural fibers
Usually excitatory, end in layers 1, 2, and 3
These are typically reciprocal connections
What are the thalamocortical inputs and what layer do they project to?
They are excitatory, end in layer 4. Include projections from VPL, VPM, VL, LGN, MGN, etc
What are the subcortical inputs to the neocortex?
They are from modulatory centers, i.e. nucleus basalis of meynert (ACh), locus ceruleus (NE), raphe nucleus (serotonin), midbrain / ventral tegmentum (dopamine).
What are the three major outputs from the cortex?
- Corticocortical
- Corticofugal
- Corticothalamic
Where do corticocortical axons project?
To other cortical layers from layers 2/3
What are corticofugal axons?
Layer 5 axons, project to subcortical targets (fugal = run from). This is for the corticobulbar / corticospinal tracts
Where does the corticothalamic tract arise?
Layer 6
What are the three types of axonal fiber bundles?
- Association
- Commissural
- Projecting
What type of imaging is used to see white matter tracts?
Diffusion tensor imaging, sensitive to the direction of water movement
What are the two types of association fibers and their general function?
- Short association fibers -> gyrus to adjacent gyrus, U-shaped fibers
- Long association fibers -> fibers interconnecting various areas of cortex
What connects the frontal lobe with the occipital and parietal lobe for eye movements?
Superior longitudinal fasciculus
What connects the frontal lobe with the posterior superior temporal lobe? What is its function and what happens if it’s lesioned
Arcuate fasciculus - involved in language function, lesion results in conduction aphasia
What is conduction aphasia?
Disconnection between Broca’s area (speech production, frontal lobe) and Wernicke’s area (speech comprehension, temporal lobe). Patients can understand speech and produce it, but the task of repeating a phrase will be particularly challenging. They also have difficulty understanding prepositional phrases (i.e. on, for, after)
They also tend to misuse words because their understanding of words is not well linked to their production of it
What is the uncinate fasciculus? Function?
Connects anterior temporal lobe with orbital part of frontal lobe, has limbic function
What is the cingulum?
Connects cingulate gyrus with parahippocampal gyrus + septal area, also has limbic function and is part of the Papez circuit
What are commissural fibers for?
Connecting left and right hemispheres, especially homologous areas of either side. Exceptions would be for eyes and hands)
What are the two places where commissural fibers pass through and what is their function?
- Corpus callosum - largest bundle
2. Anterior commissure - connects parts of temporal lobes + 2 olfactory bulbs
What are projection fibers?
Fibers passing to and from the brainstem, i.e. internal capsule
How does information travel once it enters to cortex (mainly via thalamocortical tracts)?
Input to layer 4 -> projection outwardly to layers 2,3 -> projection inwardly to layers 5,6.
This travel is radial, and creates specific columns of cells where information travels
How is the striate cortex organized?
Right and left dominance columns on one axis, then orientation of object columns on another axis. There are columns of cells which process color information “blobs”
What is the anterior boundary of the occipital lobe?
Gyri posterior to parieto-occipital sulcus all the way down to pre-occipital notch
What are the boundaries of the temporal lobe?
Superior: Lateral fissure + constructed posterior extension of lateral fissure
Posterior: extension of parieto-occipital sulcus to preoccipital notch
What separates the inferior temporal gyrus from the fusiform gyrus?
Inferior temporal sulcus
What are the boundaries of the temporal lobe?
Anterior: Central sulcus
Inferior: Posterior extension of lateral fissure
Posterior: Parieto-occipital sulcus
What is contained in the superior parietal lobule? What separates it from inferior parietal lobule?
Areas 5 and 7. Separated via the intraparietal sulcus
What is contained in the inferior parietal lobule?
Supramarginal (area 40) and angular gyri (area 39)
What are the boundaries of the frontal lobe?
Superior to lateral fissure, anterior to central sulcus
What are the 3 parts of the inferior frontal gyrus?
- Pars orbitalis
- Pars triangularis
- Pars opercularis
What is the limbic lobe?
Cingulate gyrus and parahippocampal gyrus are continuous and are often considered a separate lobe
What is the insula? What is its function?
A hidden lobe seen by prying open lateral fissure. Integrates olfactory and taste, also detects tissue / organ (visceral) homeostasis from ALS.
How does the motor homunculus differ from the sensory homunculus?
No ears representation on motor control, large hand control
How does the motor homunculus differ from the sensory homunculus?
No ears representation on motor control, large hand control
What happens in plasticity of the brain?
Other areas of cortex may contribute to performing the function that is lost when a section of cortex is lesioned.
Also, when the body is reversibly damaged, the corresponding cortex shrinks then regains normal size and function.
What is the function of the orbitofrontal gyri? Where is it located?
Located lateral to the olfactory sulcus, important in decision-making
What is the ventral anterior cingulate gyrus important with?
Mood
What does the frontal cortex (executive function) have reciprocal connections with?
DM thalamus, which influences affective behavior and perception (limbic system)
Where is Broca’s area found?
Within the pars triangularis and pars opercularis in the inferior frontal gyrus on the language dominant (Typically left) side.
What does lesion of area 4 alone cause?
Hypotonia
What does lesion of area 6 alone cause?
Apraxia, difficulty carrying out skilled tasks
What does lesion of both areas 4 and 6 cause?
Upper motor neuron symptoms (i.e. spasticity)
What does lesion of Broca’s area cause?
Expressive aphasia (Can still understand words because Wernicke’s area is intact)
What is frontal lobotomy used for?
Quieting uncontrollable patients -> destruction of executive function
What causes optic ataxia? What is it?
Lesion of superior parietal lobule (contains areas 5 and 7)
->problem in visually guided hand movements
What does lesion of the inferior parietal lobe of the non-dominant hemisphere cause?
Contralateral neglect. Usually patients will neglect left side since right hemisphere is non-dominant and lesioned in this case.
May also not dress, shave, or wear makeup on that side of the face
What does lesion of the parietal lobe of the dominant hemisphere cause?
Gerstsmann’s syndrome -> alexia (difficulty reading), acalcula (difficulty with math), agrapha (difficulty writing), left-right problems, anomia (difficulty finding a word)
What is declarative memory?
New memories which are formed in the parahippocampal gyrus + hippocampal formation
What are neurons in the hippocampus sensitive to?
Hypoxia (oxygen deprivation)
What is the medial / rostral part of the parahippocampal gyrus? What is it part of?
Uncus, part of olfactory cortex
What does epilepsy of the temporal lobe cause?
Olfactory hallucinations
What is the fusiform gyrus and what is it important for?
Occipito-temporal gyrus - important in face recognition + other sensory integration
What does fusiform gyrus lesion cause?
loss of color vision, loss of ability to perceive facial expressions, loss of face recognition (prosopagnosia) prosop = face, agnosia = ignorance
What is synesthesia?
Stimulation of sensory or cognitive pathway which leads to automatic, involuntary experiences in a second sensory or cognitive pathway (i.e. always seeing certain letters in a particular color).
Where is Wernicke’s area and what is it’s function?
The posterior part of the superior temporal gyrus (area 22) of dominant hemisphere. Functions in understanding spoken and written word?
What is receptive aphasia?
Inability to understand spoken or written word, from knocking out Wernicke’s area
What is Wernicke’s area in the non-dominant hemisphere used for?
Perceiving rhythm or emotion of speech
What is the striate cortex?
Area 17 (V1 / primary visual cortex). The association cortices are V2 and V3 (areas 18 and 19 respectively)
What causes blindsight?
Lesion of striate cortex which spares collateral pathways (unconscious), allowing patients to avoid objects in path form visual information coming from CN2. I talked to jimbo about this
What is agnosia vs stereognosia?
Agnosia - difficulty recognizing objections
Astereognosia - difficulty recognizing objects via shape
What is global aphasia?
Can’t talk or understand speech, knocked out Broca’s + Wernicke’s areas. Usually due to loss of Middle Cerebral Artery
What is aphasia?
Difficulty in using or understanding language
vs
Dysphagia -> difficulty producing words
What is apulia?
Difficulty initiating movement
What is a disconnection syndrome?
A destruction of links between information processing centers may have the same symptoms as destroying those centers?
What does singular lesion of the supramarginal gyrus cause if in the dominant hemisphere?
Brodmann’s area 40 - apraxia
What is the general function of the dominant hemisphere? What is it related to?
Comprehension + expression of language and logical thinking
Related to handedness, only 5% of right-handed are right-brain dominant vs 20% of left-handed
What is the non-dominant hemisphere?
Typically the right hemisphere, important in creativity, facial recognition, dressing, making block designs, drawing 3D cubes, etc
What test is used to assess brain dominance?
Wada test -> anesthetic in left or right carotid
What was the split brain experiment?
when right and left hemispheres cannot communicate due to damage of corpus callosum
“Face” written on the right side would travel to left brain which is normally dominant, can be understood and repeated
“Face” written on the left side would travel to the right brain which is non-dominant, cannot understand or repeat the word, but can draw it (creativity)
What are the general functions of the three major cell types of the cortex?
- Pyramidal - projecting neurons - between cortex and subcortex, contain spines
- Stellate / granular - intrinsic neurons with radiating dendrites, aspinous
- Fusiform neurons - horizontally oriented in layer 1, vertically oriented in layer 6
