Task 4 Flashcards
Subcortical fiber bundles
Subcortical fiber bundles = relay information to and from specific areas of the brain, depending on their classification as association, commissural, or projection fibers.
- Association fibers
These fibers interconnect areas of cortex within one hemisphere, with short ones connecting areas in adjacent gyri and longer ones (i.e. superior longitudinal fasciculi, cingulum, …) connecting more distant areas like different lobes.
Superior longitudinal fasciculus
= most compact in its midportion above the insula, spreads out to the anterior frontal lobe and the posterior parietal and occipital lobe, most dominant in areas responsible for language (connects all the lobes
Arcuate fasciculus
(subset of fibers) arches around the posterior end of the lateral fissure and enters the temporal lobe
Inferior occipitofrontal fasciculus
located below the insula, runs from the frontal through the temporal to the occipital lobe and therewith connects these areas.
Uncinate fasciculus
hooks around the lateral fissure to connect frontal and temporal lobe
Superior occipitofrontal fasciculus
runs adjacent and superior to the corpus callosum and interconnects the frontal, parietal and occipital lobe
Cingulum
located within the cingulate and parahippocampal gyri (limbic lobe of the limbic system) and connects areas of the limbic cortex
- Commissural fibers
These fibers connect areas from one hemisphere with their counterpart in the other hemisphere (similar functional areas) and to do that, most commissural fibers cross the midline and from the corpus callosum.
Corpus callosum
main commissural bundle that connects the two parietal lobes and the posterior parts of the frontal lobes with each other
Splenium
posterior part of the corpus callosum, interconnects the occipital lobes and the posterior temporal lobes
Genu
= anterior part, connects the frontal lobes with each other
When fibers from the corpus callosum enter the hemispheres, they
“fan out” (=radiation), which is called forceps minor (anterior) or forceps major (posterior)
Anterior commissure
small bundle of fibers that connects the anterior temporal lobes and the olfactory bulbs
Posterior commissures
located in the midbrain where it connects the two pretectal nuclei
Projection fibers
These fibers travel to or from the cortex (thalamus basal ganglia, brain stem, spinal cord). Projections come from all parts of the cortex (corona radiata) and converge into the internal capsule
Anatomy of the internal capsule
V shaped, can be divided into an anterior (between caudate and lenticular nucleus = globus pallidus and putamen) and posterior limb (between thalamus and lenticular nucleus), the place where the limbs meet is called genu (=”knee”)
Axoplasmic transport is
a process responsible for movement of organelles (mitochondria), lipids, proteins, synaptic vesicles, and other parts of the cell membranes to and from the soma down the axon to the synapses and back up to the soma
The vast majority of axonal proteins are synthesized in the
the neuronal cell body and transported along axons. Axonal transport occurs throughout the life of a neuron and is essential to its growth and survival.
Microtubules
(made of tubulin) run along the length of the axon and provide the main cytoskeletal “tracks” for transportation
Kinesin and dynein (=motor proteins)
move cargoes in the anterograde (forwards from the soma to the axon tip) and retrograde (backwards to the soma (cell body)) directions. They bind and transport several different cargoes including mitochondria, cytoskeletal polymers, and synaptic vesicles containing neurotransmitters.
Axonal transport can be
fast or slow, and anterograde or retrograde:
Anterograde transport
= movement of molecules/organelles outward, from the cell body (also called soma) to the synapse or cell membrane, for information processing to the synapse
Anterograde movement in transport vesicles of both fast and slow components along the microtubule is mediated by kinesins (= motor protein)
Retrograde transport
is movement of molecules/organelles inward, away from the synapse or plasma membrane toward the cell body or soma
Vesicles for transport of the motor proteins
(kinesin & dynactin) are sorted and loaded onto transport motors both in the cell body and the distal nerve terminal. The former are transported not only into the axon but also into dendrites.
Tracing techniques
are important for mapping connectivity between brain areas. To do so, you must carefully delineate the location of the injection site and also slice up the brain (or the part that contains the target region of interest) to create microscopic preparations that allow to visualize the amount of substances that has arrived in each slice.
tracing techniques Advantages
- Learning specifically where the input to a field comes from and where it sends output to
tarcing techniques disadvantages
- The injection site never perfectly matches the field of interest
- Substances often spread into adjacent fields
- Substance affects all neurons in the injection site with no discrimination for any segregated patch structure that might exist
Brain Connectivity and Large-Scale Brain Organization
- Focus of brain mapping shifted from functional localization toward a systematic understanding of large-scale functional organization and its influence on cognitive and affective information processing
- Most cognitive functions require multiple distributed brain regions working in concert
- Functions of individual cortical and subcortical areas are determined by their intrinsic properties and their extrinsic connections
- Understanding function of any specific brain region therefore requires analysis of how its connectivity differs from the pattern of connections in other functionally related brain areas
Mesulam (1998): Human brain includes at least five major core networks, each dedicated to a more or less distinct cognitive function
Language network anchored in the middle temporal gyrus
Working memory – executive function network anchored in the DLPFC and ventral posterior parietal cortices
Spatial attention network anchored in dorsal posterior parietal cortex and frontal eye fields
nodes
functional areas
edges
connections between them
Six Major Principles of Large-Scale Functional Organization
- Characterized by a non-random (=specific regions are localized for specific functions, areas that are next to each other have a higher probability to be connected to each other), small-world, modular global brain architecture with strategic hub regions that regulate communication among different functional systems (super optimized network similar to the fact that you know every person on the world via a maximum of 5 people)
- Strong interhemispheric connectivity between homotopic regions, with a gradient of decreasing left-right connectivity from sensory to association and heteromodal cortices. This is a prominent feature of large-scale functional brain organization.
- Human brain is intrinsically organized into coherent functional networks, with brain areas that are commonly engaged during cognitive tasks forming brain networks that can be readily identified using intrinsic functional connectivity
- Functional brain organization is characterized by task- and context-dependent activated and deactivated brain systems, pointing to bottlenecks in parallel processing and temporally restricted access to neuro resources
- Most widely deactivated regions form a coherent large-scale network, termed the default- mode network (tightly functionally and structurally connected system important for self- referential information processing and monitoring of the internal mental landscape
- Core prefrontal-parietal control system can be dissociated into distinct brain networks
Salience network
anchored in the insula and anterior cingulate cortex = plays an important role in attentional capture of biologically and cognitively relevant events
Central executive network
DlPFC VLPFC PPC (lateral parietal cortex)
= important for the working memory and higher-order cognitive processes
Graph-theoretical analysis
Whole brain as a single network and uses graph-based measures of functional or structural connectivity to characterize overall topology
o provides global snapshot of the functional architecture of the brain
• Studies have shown that the brain has a small-world architecture characterized by dense local clustering of connections between neighbouring nodes and a short path length between nodes, due to the existence of relatively few long-range connections
Small-world architecture
network in which constituent nodes exhibit a large degree of clustering and relatively short distances between any two nodes of the system and is thought to reflect a balance between local processing and global integration of information
efficient, minimized wiring costs
high specialization and high integration within a modular architecture
• Hubs
= brain areas (nodes) that are central to communicating information across different brain systems within a small-world architecture
functional role can vary widely depending on connectivity properties
o Posterior cingulate cortex = shortest path length to other brain areas; facilitates the rapid integration of information across multiple functional systems
o Insula = connector hub that links different subnetworks
• Strength of interhemispheric connectivity is not uniform across the brain
• Highest correlations across primary sensorimotor cortices
• Lower correlations across unimodal association areas
• Even lower correlations across heteromodal association areas
because of increased functional lateralization and specialization of these regions
• Brain is intrinsically organized into
large-scale brain networks that facilitate segregation and integration of functional systems and impose constraints on signalling and information processing
Default-Mode Network
Default network is a deactivated network (active when relaxed – when we are “deactivated” like daydreaming or chillin’)• Anchored in the posterior cingulate cortex and ventro-medial PFC, with prominent nodes in the medial temporal lobe and the angular gyrus
• Comprises an integrated system for autobiographical, self-monitoring value judgments, and other cognitive functions that support self-referential mental activity • Key nodes linked to episodic memory retrieval, autobiographical memory, and internal speech
• Specific nodes in medial PFC à self-related and social cognitive processes, value-based decision making, and emotion regulation
• Construction of mental models of personally significant events
• Abnormalities in psychiatric disorder including Alzheimer’s, schizophrenia, and depression, in which self-related processing and monitoring are known to be disrupted
Salience network
anchored in the anterior insula and ACC; strong links with paralimbic and limbic areas • Integrates brain signals involved in conflict monitoring, interoceptive-autonomic, and reward-processing areas into a common “salience network”
• Identify the most homeostatically relevant stimuli in order to guide behaviour
• Attentional capture of biologically and cognitively relevant “salient” events and then signalling other brain systems, including the frontoparietal central executive network, for additional, more sustained, goal directed processing
Central executive networks
amodal system, anchored in the DLPFC and VLPFC and the supramarginal gyrus in the lateral parietal cortex
• Lacks connectivity with limbic, hypothalamic, and midbrain structures
• Critical for actively maintaining and manipulating information in the working memory, for rule-based problem solving, and for decision-making in the context of goal-directed behaviour
Dynamic interactions between these networks regulate shifts in attention and access to goal-relevant cognitive resources
When salience network is active
the default network is inactive
The salience network allows us to
switch between the default network to the central executive network
- We are daydreaming in a lecture default network is active
- Then we hear a word that sounds important to us BOOM salience networks kicks in and tells you to pay attention,
- If needed then (when the task is complex and requires working memory) the central executive network is activated by the salience network
DEFAULT
VMPFC
PCC
Self-mediated mental activity
Active while chilling
SALIENCE
Anterior insula (AI) Anterior cingulate cortex Conflict monitoring & attention Reward processing & emotion Allows transition between networks
CENTRAL EXECUTIVE
DLPFC
VLPFC
PPC (lateral parietal cortex)
Monitoring and manipulation of information in WM
Problem solving
Decision making for goal-directed behaviour
6 layers within cortex
- molecular layer
- external granular layer
- externalpyramidal layer
- Internal granular layer
- Internal pyramidal layer
- multiform layer
primary sensory cortex
few pyramidal many granular
granual neurons
kind a like interneurons
Agranular cortex
motor cortex: a large number of pyramidal neurons (output), a few granular
Short association fibers
connect areas in adjacent gyri or sulci
multiform layer (layer 6)
and contains output neurons of varying shapes and sizes
Layer 1 is the molecular layer
and contains mainly neuronal processes
Anatomy of the internal Capsule
It is V shaped in horizontal section:
Anterior limb – between the caudate and the lenticular nucleus (putamen and globus pallidus)
Corticopontine and thalamocortical fibers from the dorsomedial and anterior nuclei of the thalamus that project to the frontal cortex
Posterior limb- between the thalamus and the lenticular nucleus
Contains corticopontine, thalamocortical and corticospinal fibers
Genu – point where the two limbs meet
Global brain architecture
Graph-theoretical analysis of connectivity across the entire brain views the whole brain as a single network
The brain has a small world-architecture:
a) Dense clustering of connections between neighboring nodes
b) Short path length between the nodes
Reflects a balance between local processing and global integration of information
They are economic, minimize wiring costs while supporting efficient processing of complex information
Promote high specialization and high integration
Hubs – brain areas that are central to communicating information across different brain areas
a) Posterior cingulate cortex – shortest path length to other brain areas (facilitate the rapid integration of information across many systems)
b) Insula – connector that links different subnetworks
Graded Inter- and intrahemispheric connectivity’s
Homotopic regions in left and right hemisphere display strong interhemispheric interactions when compared with nonhomotopic regions
The strength of connectivity is not uniform across the brain:
1. Primary sensory cortices – high connectivity
2. Unimodal association areas – lower
3. Heteromodal association areas – even lower
This is consistent with the functional lateralization and specialization of these regions
Left and right hemisphere connectivity differ in important ways:
Left: bias toward stronger intrahemispheric connectivity, particularly for cortical regions involved in language and motor coordination
Right: interhemispheric connectivity with homologous regions in the left hemisphere, especially for visuospatial and attentional processing
CYTOARCHITECTURE
The cortex is organized into functional units (cortical columns) which are specialized to process specific inputs or outputs
The cytoarchitecture of the columns differs depending on their function (input vs. output)
Broadmann
found 43 distinct areas in human
the names of the people that found more than broadmann?
????
broadman critics
- Lack of observer independency, reproducibility and objectivity (researchers tried to do the same as Brodmann and failed to distinguish the areas)
- Individual variation in the architectonic structure of areas similarly located in different specimens of the same species
- Inter subject variability
- fmri show maps i not complete ,sometimes wrong- his model is 2d
multi-receptor mapping
ausgleicht broadmann + add them to broadmann map
a) Anterograde
mediated by kinesis
b) Retrograde
mediated by dynein (recycling many of the substances found at the synaptic ending and informs the soma of conditions at the axons terminals
cargoes
mitochondria, cytoskeletal polymers, vesicles with NTM
