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Functional Neuroanatomy > TASK 4 - CERBRAL CORTEX > Flashcards

TASK 4 - CERBRAL CORTEX Flashcards

1
Q

cerebral cortex

A

= body’s ultimate control + information processing centre

  • consists mainly of cell bodies + capillaries –> grey matter
  • cerebrum’s outer layer of neural tissue
  • folded: evolutionary growth, but skull limited this growth
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2
Q

structural organisation

1. cortices

A

a) iso-/neocortex: 6 layers (I to VI)
- enables us to be thinking individuals
b) allocortex: 3-4 layers
- archicortex = hippocampus
- paleocortex = olfactory bulb

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3
Q

structural organisation

2. layers

A

layer I = molecular layer (neuronal processes)
layer VI = multiform layer (output neurons)
1. pyramidal neurones = main output cells of cortex; triangular structure, typically one apical dendrite and abundant dendritic trees from cell body
- layer III & V
2. granular neurones = stellate neurones = main interneurons; shorter axons + smaller dendritic trees
- layer II & IV
- granular cortex = S1 = large number of granular neurones
- agranular cortex = M1 = not many granular neurones

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4
Q

structural organisation

3. cytoarchitecture/ columns

A

= neurones in layers connect vertically to form small mini circuits

  • functional units = cortical columns specialised for specific inputs + outputs
  • cytoarchitecture of columns differs depending on their function
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5
Q

Brodmann’s areas

A
  • Brodmann found areas with different histological organisations
  • -> later Penfield found that these areas correlate with functionally different areas
  • human cortex: 43 cytoarchitectonic areas (monkeys & apes only have about 30)
  • each area in human brain has a number between 1 and 52
  • -> left out 12-16 & 48-51: not identifiable in human cortex (e.g. olfactory, limbic & insular cortices)
  • 1,2,3: somatosensory
  • posterior part of 22: Wernicke (auditory)
  • pioneering piece of work in the field + still has great impact
  • basis for ongoing analysis of the relation between function, cortical structure
  • -> nowadays advances with DTI + fibre tracking
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6
Q

Brodmann’s areas

- problems

A
  • cerebral cortex was over-parcellated
  • lack of observer independency, reproducibility + objectivity
  • lack of data on inter-subject variability –> maps must be probabilistic rather than a given map
  • map is sometimes incomplete (regions of occipital lobe)
  • -> 2/3 of cortex are not visible due to sulci/gyri = only 1/3 described
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7
Q

intersubject variability

A

= brains differ between different individuals (= inter-individuality)

  • need for spatial normalisation
  • cortex surface-based approach: cortex-based alignment of individual brains (lecture: kugel)
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8
Q

structural organisation

4. cortical connections

A
  • relay information to & from specific areas of the brain
    a) association fibres
    b) commissural fibres
    c) projection fibres
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9
Q

4a. association fibres

A

= connect cortical areas WITHIN hemispheres

  • short association fibres = connect areas in adjacent gyri
  • long association fibres = connect more distant areas
    1) superior longitudinal fasciculus = connects frontal, parietal + occipital lobes; above insula
  • arcuate fasciculus = arches around posterior end of lateral fissure and enters temporal lobe –> connects frontal, parietal, temporal lobes (in dominant hemisphere connects two major language areas)
    2) inferior occipitofrontal fasciculus = connects frontal through temporal to occipital lobes; below insula
  • uncinate fasciculus = hook around margin of lateral fissure; connects frontal + temporal lobe
    3) superior occipitofrontal fasciculus = connects frontal, parietal + occipital lobes
  • runs adjacent and superior to corpus callosum
    4) cingulum = connects areas of limbic system with each other; located within limbic lobe (cingulate & para-hippocampal gyri)
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10
Q

4b. commissural fibres

A

= connect similar/same functional areas BETWEEN hemispheres

  • enable coordination of cortically activity across hemispheres; integrate information to function as one unit
    1) corpus callosum = largest cortical commissure; where majority of commissural fibres in brain cross midline
    1a) genu = anterior pole; connects frontal lobes with each other
    1b) body = parietal lobes + posterior frontal lobes
    1c) splenium = posterior pole; interconnects occipital + posterior temporal lobes
  • as fibres from corpus callosum enter hemispheres, fan out to reach all parts of cortex
  • -> forceps minor = at the anterior end
  • -> forceps major = at the posterior end
    2) anterior commissure = connects anterior temporal lobes + olfactory bulbs
    3) posterior commissure (midbrain) = connects pretectal nuclei
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11
Q

4c. projection fibres

A

= travel to + from the cortex

  • from all parts of the cortex in corona radiata –> converge into internal capsule
  • internal capsule = compact bundle; V shaped in horizontal section
  • anterior limb = between caudate + lenticular nucleus
  • -> corticopontine and thalamocortical fibres (from dorsomedial + anterior nuclei of thalamus –> to frontal cortex)
  • posterior limb = between thalamus + lenticular nucleus
  • -> corticopontine, thalamocortical, corticospinal fibres
  • genu = where two limbs meet
  • -> corticobulbar fibres
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12
Q

axoplasmic transport

A

= process responsible for movement of organelles (mitochondria), lipids, proteins, vesicles and other parts of the cell between the soma & the synapses

  • most stuff synthesised in cell body/soma
  • transported in vesicles
  • essential for growth + survival
    1. anterograde transport = soma –> synapse/cell membrane (= outward movements)
  • motor protein: kinesin (mediates movement)
  • -> proteins are the motor of movement; microtubules provide tracks for motor
  • fast & slow
    2. retrograde transport = synapse/plasma membrane –> soma (= inward movements)
  • motor protein: dynein
  • recycling & info about conditions at axon terminals
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13
Q

tracing

A
  • important for mapping of connectivity between brain areas
  • figure out the pathways
    1. delineate location of injection site
    2. slice the brain (at least part that contains the target region)
    3. create microscopic preparations –> allow to visualise amount of substances that has arrived in each slice
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14
Q

tracing

- pros + cons

A

√ learn specifically where the input to a field comes from & where it sends its output to

x injection site never perfectly matches the field of interest
x substances often spread into adjacent fields
x substance affects all neurones in the injection site –> no discrimination of any segregated patch structure that might exist

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15
Q

large-scale functional organisation

A

= insight into how intrinsic functional architecture of the brain facilitates segregation of neural signals + allows flexible interactions for goal-directed behaviour

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16
Q

large-scale functional organisation

1. global brain architecture

A

= non-random small-world organisation
- optimal connectivity for synchronisation + information transfer with minimal rewiring cost
= in a large group, it is possible to connect some more close —> initially long connection becomes short connection through short links/edges
- nodes = functional brain areas; individual neurones
- hubs = nodes that are most important in a network; receives a lot of info, sends the most info
- modular organisation = network is organised into dense neighbourhoods; more connected within a system, less connected to out-groups

17
Q

large-scale functional organisation

2. interhemispheric connectivity

A

= modular architecture dominated by strong interhemispheric connectivity between homologous regions

  • heterogenous regions are not as strongly connected because their function is lateralised + specialised (e.g. language areas)
  • connections are decreasing from sensory to heterogenous
18
Q

large-scale functional organisation

3. coherent functional networks

A

= intrinsically organised into multiple coherent networks

  • segregate specific signals to functional systems + constrain information processing
  • 14 functional networks (e.g. auditory, basal ganglia, sensorimotor…) that are spatially segregated
  • coactivated for many tasks: nodes of networks can flexibly interact to facilitate cross network signalling
19
Q

large-scale functional organisation

4. activation and deactivation

A

= areas that show common patterns of activation & deactivation are organised into distinct intrinsic brain systems

  • impose bottlenecks due to network access, conflict + resources
  • neural resources you need (relevant) is filtered —> goes into bottle —> what is unnecessary falls out of bottle
  • cannot process everything at ones —> neural resources are limited
  • if you put a lot of energy into one area (activate) —> deactivate another (antagonistic nature)
20
Q

large-scale functional organisation

5. default-mode network

A

= most commonly deactivated brain regions form a default-mode network

  • posterior cingulate cortex + medial prefrontal cortex
  • functional brain system
  • important for self-referential information processing
21
Q

large-scale functional organisation

6. fronto-opercular-parietal brain regions

A

= implicated in a wide range of cognitive task (incl. cognitive control)
- form dissociable, intrinsic functional systems that play distinct roles in cognition + control

22
Q

large-scale functional organisation

6a. salience network

A

= transient attentional capture of biologically + cognitively relevant (= salient) events (= filter)

  • anterior insula + ACC
  • signals other brain systems for additional, more sustained, goal-directed processing
  • insula = hub
23
Q

large-scale functional organisation

6b. central executive network

A

= more sustained goal-relevant & adaptive processing (e.g. maintaining & manipulating info in WM)

  • DLPFC & PPC (= supramarginal gyrus)
  • dynamic interactions between these networks regulate shifts in attention + access to goal-relevant cognitive resources

Functional Neuroanatomy (5 decks)

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