TASK 4 - CERBRAL CORTEX Flashcards
cerebral cortex
= 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
structural organisation
1. cortices
a) iso-/neocortex: 6 layers (I to VI)
- enables us to be thinking individuals
b) allocortex: 3-4 layers
- archicortex = hippocampus
- paleocortex = olfactory bulb
structural organisation
2. layers
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
structural organisation
3. cytoarchitecture/ columns
= 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
Brodmann’s areas
- 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
Brodmann’s areas
- problems
- 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
intersubject variability
= brains differ between different individuals (= inter-individuality)
- need for spatial normalisation
- cortex surface-based approach: cortex-based alignment of individual brains (lecture: kugel)
structural organisation
4. cortical connections
- relay information to & from specific areas of the brain
a) association fibres
b) commissural fibres
c) projection fibres
4a. association fibres
= 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)
4b. commissural fibres
= 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
4c. projection fibres
= 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
axoplasmic transport
= 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
tracing
- 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
tracing
- pros + cons
√ 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
large-scale functional organisation
= insight into how intrinsic functional architecture of the brain facilitates segregation of neural signals + allows flexible interactions for goal-directed behaviour
large-scale functional organisation
1. global brain architecture
= 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
large-scale functional organisation
2. interhemispheric connectivity
= 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
large-scale functional organisation
3. coherent functional networks
= 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
large-scale functional organisation
4. activation and deactivation
= 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)
large-scale functional organisation
5. default-mode network
= 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
large-scale functional organisation
6. fronto-opercular-parietal brain regions
= implicated in a wide range of cognitive task (incl. cognitive control)
- form dissociable, intrinsic functional systems that play distinct roles in cognition + control
large-scale functional organisation
6a. salience network
= 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
large-scale functional organisation
6b. central executive network
= 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
