L2 - Physiology

Question 1

What is the difference between signalling and non signalling processes?

Answer 1

• Signalling processes refer to intraneuronal (AP production) and interneuronal (neurotransmission) communication
• Nonsignalling processes refer to housekeeping needs (biosynthesis or proton leaks) and maintenance of resting membrane potential. They do not significantly change with brain activity.

Question 2

How much energy does the brain require relative to other body parts?

Answer 2

10x the amount of energy per unit of body weight compared to other body parts

Question 3

How does energy expenditure differ between grey matter and white matter?

Answer 3

• Grey matter: Signalling processes dominate ATP demand (20% for inhibitory processes and 80% for excitatory – 70% total)
• White matter: Non-signalling processes dominate ATP demand (30% total)

Question 4

Explain the difference between energy expenditure in a human and a rat.

Answer 4

• AP: 3.3x higher in human
• Maintenance of resting potential: 2.6 x higher in human
• Glucose metabolism: Lower in humans
• At any one time, there are fewer neurons active in human cortex than rat cortex. This is because neural coding processes are more efficient and evolved in humans. They are designed to preserve energy for when it is needed.

Question 5

What are the 4 outcomes of experimental degradation of the ECM?

Answer 5

• Improving post-traumatic regeneration in the brain
• Restoring ocular dominance plasticity
• Facilitating fear extinction
• Enhancing cognitive flexibility in reversal learning

Question 6

What are the 4 systems-analysis approaches to studying cortical physiology? Give an example of each.

Answer 6

1. Neurotransmitter-based approaches (e.g. depleting dopamine in the nigra-striatal system)
2. Small scale network-based approaches (early sensory / perceptual processing)
3. Large scale network-based approaches (fMRI)
4. Cognitive style-based approaches (Type 1 and Type 2 thinking)

Question 7

Explain the difference between exaptation and adaptation.

Answer 7

• Exaptation: An adaptive feature turned out to be useful for some other reason as well.
• Adaptation: Change in a structure due to random genetic mutations that turned out to be adaptive.

Question 8

Explain how the similar neural organization of the posterior and anterior cortices provide evidence for exaptation.

Answer 8

• Older posterior cortex and newer anterior cortex both have columnar organizations
• Goal-directed cognition is evolutionary descendant of spatial foraging capacity in higher animals
• Navigation of “internal” space relies on control of attention between exploration and exploitation
• Spatial foraging capacity is the ability of animals to locate and remember sources of food while goal-directed behaviour is the ability to think of something for a purpose
• Neural physiology involved in area-restricted search might also exist more anteriorly in order for us to “search our minds”, i.e., go back in time mentally.

Question 9

What are the three types of communicating tracts in cortical networks?

Answer 9

1. Projection (cortical/subcortical connections) – M1 to BG
2. Association (connections within a hemisphere)
3. Commissural (connections between hemispheres) – CC, anterior commissure

Question 10

Explain the difference between a “node” and an “edge” of a cortical network.

Answer 10

• Node: A group of brain areas jointly and uniquely activated or deactivated during a cognitive function relative to a baseline state.
• Edge: A connection between nodes that represents the degree of influence a structure has on other structures it communicates with.

Question 11

What is a network scale? Differentiate between large-scale and small-world networks.

Answer 11

• Network scale: Refers to the number of nodes (N) and average degree (k) of a network
• Large-scale: Collections of widespread cortical regions showing functional connectivity, defined by temporal correlation of tight physical coupling by tracts (e.g. retino-geniculate cortical pathway)
• Small-world: Lots of nodes in close proximity with short connections amongst them, 6 degrees of separation (e.g. retina)

Question 12

Explain the metabolic activity of the default mode network.

Answer 12

• Brain regions have lower activity during goal-directed cognition or when a person is engaged in a task requiring externally-directed attention
• Brain regions have higher metabolic activity when awake and involved in mental processes involving low attentional demands

Question 13

What are the 6 brain regions identified in the DMN?

Answer 13

1. Medial PFC
2. Posterior cingulate cortex
3. Inferior parietal lobule
4. Lateral temporal cortex
5. Dorsal medial PFC
6. Hippocampal formation

Question 14

Compare and contrast Type 1 and Type 2 thinking.

Answer 14

• Type 1: DMN (spontaneous cognition). Responsible for thinking using internal representations (daydreaming), memory recall, envisioning the future, monitoring the environment, and thinking about the intentions of others. This thinking is fast and occurs without effort.
  Type 2: Executive Control Network (LH for planning and decision making; RH for executive control of attention). Responsible for error correction and troubleshooting, novel sequences of action, dangerous or difficult situations, situations that involve overcoming habits or temptations.

Question 15

What is the Salience Network?

Answer 15

• Large-scale network composed of the anterior insular and dorsal anterior cingulate cortex that are linked by the uncinate fasciculus
• Both nodes have von Economo neurons (associated with consciousness)
• Modulates switch between internally-directed cognition and externally-directed cognition (DMN and Executive Control).

Question 16

What is the Sensorimotor Network?

Answer 16

• Large-scale network that includes the somatosensory and motor regions
• Activated during complex motor tasks involving learned behaviours

Question 17

What is the Auditory Network?

Answer 17

• Cortical regions associated with auditory information processing
• Primary and secondary auditory cortex, association cortex in temporal lobe, PFC
• Networks different between each hemisphere

Question 18

What are the two visual networks?

Answer 18

• Visual Lateral: Involved in complex emotional stimuli via vision (e.g. recognizing emotion by someone else’s facial features)
• Visual Occipital: Associated with early processing of information from retinocortical pathway (figure-ground segregation, colour, motion)
• Collaterals from thalamus project to cortical Layer 1

Question 19

Explain how neuron density changes across the cortex.

Answer 19

• Posterior cortex is denser than anterior cortex, which suggests a more rigid structure / function relationship in physiologically older regions
• In posterior cortex, it is rare to find low resting level while some neurons in anterior cortex don’t have resting firing rates at all
• Neural density and flexibility of function are inversely related

Question 20

Explain how irregularity of firing in the PFC may allow for more complex behaviour.

Answer 20

• Rule learning requires activity from the PFC, which largely consists of association cortex
• Therefore, learning requires writing over non-functional cortical areas that largely consist of interneurons (no direct input from sensory systems or output to motor systems)
• Involves selectively processing and integrating various kinds of information
• Neural organization of the posterior brain is fixed: When you see a visual illusion, you can usually only see one image at a time. Flipping back and forth requires lots of effort. This may be due to rigid organization of the cortex.
• Decision making is more flexible and change can occur with less effort.
• Irregularity of neuronal firing patterns made possible an increased rate of neural network state transitions
• With a regular firing pattern, small fluctuations in firing don’t change the state of the network because there is too much constraining it. However, firing irregularities reflect state transitions in frontal areas of brain.