L11 Global Brain Activity

Question 1

give some examples of a rhythmic environment

Answer 1

• temperature, day and night, tides…

Question 2

describe Brain rhythms

Answer 2

sleeping and waking, breathing cycles, steps of walking, stages of night sleep

Question 3

what is the Electroencephalogram (EEG)

Answer 3

Physiology of sleep

Epilepsy

Question 4

what does the EEG detect

Answer 4

• Generation of small fields in pyramidal cells

- thousands of them-activated together

Question 5

what are the basic requirements for detection in the Electroencephalogram (EEG)

Answer 5

1) A whole population of neurons must be active in synchrony to generate a large enough electrical field at the level of the scalp.
2) This population of neurons must be aligned in a parallel orientation so that they summate rather than cancel out.

Question 6

what is the relationship between synchronous activity and the EEG

Answer 6

The amplitude of the EEG signal partly depends on how synchronous the activity of the underlying neurons is.

Number of active cells, total amount of excitation, timing of activity.

Question 7

what type of EEG/Brain rhythms correlate with pathology & behavioural states

Answer 7

1) The alpha rhythm, 8-13Hz, awake subjects with eyes closed
2) The beta rhythm, 14-60 Hz, indicates mental activity and attention, eyes open
3) Theta waves, 4-7 Hz, indicates drowsiness and sleep or a pathological condition.
4) Delta waves, <4 Hz, as in 3.

Question 8

how are synchronous rhythms generated

Answer 8

a) Leader and band, analogous to pacemaker

b) ~ Jam session, improvisation, the timing arises from the collective behaviour of the neurons themselves.

Question 9

describe the generation of synchronous rhythms (a) in more depth

Answer 9

A one neuron oscillator:

• Thalamic cells have a set of voltage-gated ion channels that allow each cell to generate rhythmic, self-sustaining discharge patterns, even in the absence of external inputs.
• The rhythmic activity of each thalamic pacemaker neuron then becomes synchronised with many other thalamic cells via a hand-clapping kind of collective interaction.

Question 10

what are the functions of brain rhythms

Answer 10

• Sensory input – thalamus – cortex
• Activity coordination (binding) of different cortical regions (synchrony, oscillations)

Meaningless by-product of feedback circuits and connections

Question 11

what are the 4 behavioural criteria for sleep

Answer 11

Reduced motor activity

Decreased response to stimulation

Stereotypic postures

Relatively easy reversibility

Question 12

go over slide 16 for the 3 functional states of sleep

Answer 12

how was it

Question 13

what is the function of sleep and dreaming

Answer 13

Conservation of metabolic energy

Cognition

Thermoregulation

Neural maturation and mental health

Question 14

describe the imaging techniques useful for this theme???

Answer 14

A)Structural imaging: Measures of the spatial configuration of types of tissue in the brain (static maps)

1) Computerised tomography, CT
2) Magnetic resonance imaging, MRI

B)Functional imaging: Measures the moment-to-moment variable characteristics of the brain that may be associated with changes in cognitive processing (dynamic maps)

1) Positron emission tomography, PET
2) Functional magnetic resonance imaging, fMRI

Question 15

what is the basic physiology underpinning functional imaging

Answer 15

• The brain makes up 2% of the body weight, but consumes 20% of the body’s oxygen uptake; it can’t store oxygen and only stores little glucose.

Oxygen and energy needs are constantly met by the local blood supply. When the metabolic activity of neurons increases, then the blood supply to that region increases as well.

PET measures change of blood flow to a region.

fMRI is sensitive to the concentration of oxygen in the blood.

Because of constant activity, we always compare an experimental condition with a baseline condition (before and during performance).

Indirect measures of neuronal activity

Question 16

describe PET

Answer 16

Based on blood volume
Involves radioactivity (signal depends on radioactive tracer)
Participants scanned once or few times
Temporal resolution: 30”
Effective spatial resolution: 10mm
Sensitive to the whole brain
Can use pharmacological tracers

Question 17

describe BOLD MRI

Answer 17

BOLD) fMRI
Based on blood oxygen concentration
No radioactivity (signal depends on deoxyhaemoglobin levels)
Participants scanned many times
Temporal resolution: 1-4”
Spatial resolution: 1mm
Some brain regions (e.g. near sinuses) are hard to image

Question 18

describe CT scans

Answer 18

Based on the amount of X-ray absorption in different types of tissue.
Bone absorbs the most (the skull appears white), cerebrospinal fluid absorbs the least (the ventricles appear black) and the brain matter is intermediate (grey).
Used in clinical settings, e.g. to diagnose tumours or identify haemorrhaging or other gross brain anomalies.

Question 19

describe MRI

Answer 19

MRI
2003 Nobel prize to Sir Peter Mansfield and Paul Lauterbur.
Completely safe, so people can be scanned many times.
Provides a much better spatial resolution.
Provides better discrimination between white and grey matter.
Can be adapted for detecting the changes in blood oxygenation associated with neural activity (fMRI).