Chapters 17 18 Single

Cerebral Cortex „

Neocortex … …

„

Paleocortex … … …

„

6 layers Recent phyolgenetically 3 layers Older Insular cortex, piriform cortex, primary olfactory cortex

Archicortex … … …

3 layers Older Hippocampal formation

Microscopic structure „

Principal neurons … Aka

projection … Pyramidal … Fusiform … Excitatory

Microscopic structure „

Interneurons … Stellate

Aka granule „ Small „ Extensive dendritic tree „ Layer IV „ Excitatory interneuron „

Microscopic structure „

Interneurons … Horizontal

Layer I „ Development & neonatal „

… Martinotti

Multipolar „ Axon ascends „ Deep layers „

Cortical Layers „

Layer I – Molecular … Mostly „

processes

Axons and dendrites

… Sparse

interneurons „

Horizontal cells

… Neuroglia … Synaptic

area

Cortical Layers „

Layer II – External granular … Dense … Small

and mediumsized pyramidal & interneurons … Axons and dendrites „ „ „

Coming here Passing through Pyramidal … …

Dendrites extend to Layer I Axons project to deeper layers

… Intracortical

circuitry

Cortical Layers „

Layer III – External Pyramidal … Larger

pyramidals

Dendrites -> Layer I „ Axons -> deeper layers, contralateral, extracortical projections „

… Receives

axons from other cortical & extracortical areas

Cortical Layers „

Layer IV – Internal Granular … Pyramidal

cells … Stellate/Granule cells … Densest layer … Best developed in primary sensory areas … Input layer … V1 „

Stripe of Gennari …

„

Dense band of horizontally oriented thalamocortical nerve fibers

Hence striate cortex

Cortical Layers „

Layer V – Internal Pyramidal … … … … … …

…

Large & medium-sized pyramidal cells (largest) Stellate cells Cells of Martinotti Least dense Dendrites project to superficial layers Axons to mainly: subcortical, and to other cortical areas Output layer

Cortical Layers „

Layer VI – Multiform … Variety

of cells of different sizes … Primary location of Martinotti cells

Cortical Layers „

Paleocortex & Archicortex … Layers

„

Neocortex … Layers

„

I, V, VI I-VI

Columnar organization … Modules … Inhibit

nearby modules … Critical periods „

Increase synaptic connections

Inputs „

Thalamus … Modality „

specific

Layer IV

… Nonspecific „

Project diffusely

Inputs „

Extrathalamic modulatory … Serotonergic … Dopaminergic … Noradrenergic … Histaminergic … Cholinergic … GABAergic

Inputs „

Association Fibers … From

same hemisphere … Short „

Nearby regions

… Long „

Distant regions

Inputs „

Association Fibers … Long „

Superior longitudinal fasciculus …

„

Arcuate fasciculus …

„

Frontal lobe with other 3 Frontal -> speech areas

Cingulum … …

Core of the cingulate gyrus Frontal -> parahippocampal gyrus

Inputs „

Commissural fibers … From

other hemisphere … Corresponding and non-corresponding regions … Travel via corpus callosum

Inputs „

Specific thalamocortical … Mostly

„

Nonspecific thalamocortical … Diffuse

„

layer IV

all layers

Association Fibers … Laminae

„

I-III

Commissural Fibers … Laminae

I-III

Outputs „

Association Fibers … Short „

Layer II

… Long „

„

Layers III & V

Commissural Fibers … Layer

III

Outputs „

Corticofugal … Output

to subcortical structures Corticospinal „ Corticoreticular „ Corticobulbar „ Corticopontine „ Corticothalamic „ Corticohypothalamic „ Corticostriate „

Corticospinal Tract „

„ „

Cortex to motor neurons in the spinal cord Skilled volitional movements Pyramidal cells in Layer V … Primary

motor, premotor, somatosensory areas

Corticoreticular Tract „

Cortex to reticular formation in brainstem … Bilateral

„ „ „

projections

Predominantly from motor, premotor, somatosensory areas Accompanies corticospinal tract Many fibers continue to brainstem nuclei [cranial nerves], thus forming corticoreticulobulbar tract

Corticobulbar Tract „

Motor cortex (face representation) -> motor nuclei of cranial nerves …

„

Trigeminal, facial, glossopharyngeal, vagus, accessory, hypoglossal

5 face representations …

M1, supplementary motor (M2), rostral cingulate gyrus (M3), caudal cingulate gyrus (M4), ventral lateral premotor cortex (LPMCv)

Corticopontine Tract „

Cortex (frontal, parietal, occipital) -> pontine nuclei … Lesions „

Contralateral ataxia

Corticothalamic Tract Cortical areas that receive thalamic input „ Feedback „ Reciprocal connections „

Corticohypothalamic Tract Cortex -> hypothalamus „ Primarily from prefrontal cortex, cingulate gyrus, amygdala, olfactory cortex, hippocampus, septal area „ i.e. decisions, emotions, memory „

Corticostriate Tract „

Cortex -> striatum … Direct … Indirect „ „ „

…3

via

Corticothalamostriate Corticopontine -> collaterals Corticoolivary -> collaterals

zones: „ „ „

Sensorimotor Associative Limbic

Intracortical Circuitry

Cytoarchitecture „

Architecture of the layers … Thickness

of cortex … Width of the different layers … Cell types in each layer … Cell density in each layer … Nerve fiber lamination „

Define areas based on this … Brodmann

areas: 52 of them

Primary Somatosensory Area (S1) „ „ „ „ „ „

Postcentral gyrus Brodmann areas 1-3 Cutaneous: Touch, pain, temperature Proprioceptive: position, vibration, 2-point discrimination Input from thalamus, commissural, short association (M1) Outputs: M1, contralateral S1, association somatosensory cortex (area 5 & 7), thalamus, medulla, dorsal horn of spinal cord

Primary Somatosensory Area (S1) „

Area 1 … Cutaneous

or proprioceptive

„

Area 2 & 3A … Proprioceptive

„

Area 3B … Cutaneous

Somatosensory Homunculus „

Body Representation

Secondary Somatosensory Cortex (S2) „

Body representation …

Bilateral … Reverse of S1, so faces are next to each other … Receptive fields „ „

„

Lesions …

Asymbolia for pain „

„

Large Bilateral

Feel pain, but don’t respond to it.

Function: conscious perception of noxious stimuli

Somatosensory Association Areas „ „

Perception of shape, size, texture Stereognosis …

„

Identification of objects by contact

Area 5 …

Goal-directed voluntary movements … Manipulation of objects „

„

Tool use/body image

Area 7 …

Integration of visual and somatosensory stimuli „ „

Hand-eye coordination Fake arm study

Primary Visual Cortex (V1) Surface of the occipital lobe & calcarine sulcus „ Area 17 „ Striate cortex „

… Band

of Gennari

Inputs to V1 „

Retina to LGN … Via

optic nerve, optic chiasm, optic tract

„

LGN to V1 … Via

optic radiations

V1: Visual Field Representation „ „

Contralateral Visual Field Contralateral Eye: … Nasal

retina projections cross at optic chiasm

„

Ipsilateral Eye: … Temporal

retina projections pass straight through

V1: Central vs Peripheral „

Central: … Macula „

Fovea

… Cones

and Rods … Occipital surface „

Peripheral … Mostly

Rods … Calcarine sulcus

V1: Superior vs Inferior Visual Field „

Lower Visual Field … Superior

retina … Superior part of visual cortex „

Upper Visual Field … Inferior

retina … Inferior part of visual cortex

V1 Cortical magnification „ Phosphenes „ Cortical blindness „

… Blindsight

„

Lesions: … Can

be macular-sparing

Vascular damage to calcarine sulcus „ Occipital surface spared „

Extrastriate Cortex „ „

Later stages of visual processing 2 pathways … Ventral: „

‘What’

… Dorsal „

„

‘Where’

Lesions cause various disorders … Prosopagnosia … Akinetopsia

Primary Auditory Cortex (A1) Superior temporal gyrus „ Areas 41 & 42 „ Input from medial geniculate nucleus „ Stimulation „

… Tinnitus „

Buzzing, humming, knocking

A1: Outputs Auditory association cortices „ Contralateral A1 „ S1 „ FEF „ Broca’s area „ MGN „

Auditory Association Cortex „ „

Area 22 Wernicke’s area (dominant hemisphere) … Comprehension

of speech

… Lesion „

Receptive aphasia …

„

Cannot comprehend spoken words

Nondominant hemisphere … Non-speech „ „ „

Environmental sounds Musical melodies Tonal qualities

Primary Gustatory Cortex Area 43 „ Parietal operculum „ Taste „ Input from posteroventral medial nucleus of the thalamus „

Primary Olfactory Cortex „

Piriform cortex … Tip

of temporal lobe

Input bypasses thalamus „ Discriminates different odors „

Primary Vestibular Cortex Lateral cortical temporoparietal area „ Lesions „

… Impair

preception of body orientation and movement

Cortical Motor Areas Primary Motor (M1) „ Supplementary Motor Area (SMA/M2) „ Premotor area (PMv and PMd) „