Lecture 32

Question 1

Explain the importance of synchronization in neuronal communication

Answer 1

• synchronization boosts information transfer between brain regions
• create oscillations which create windows of high and low excitability, where neurons are more or less likely to fire, creating preferred time windows for communication between brain areas. Modulates neurons response to input and likelihood of spike production

Question 2

What is phase locking?

Answer 2

when two or more neuronal groups fire in sync

Question 3

What happens if all neurons are synchronized?

Answer 3

• it results in global phase locking which is often seen in epilepsy and is incompatible with normal brain function

Question 4

What functions are brain oscillations and synchronization associated with?

Answer 4

perception, cognition, motor tasks

Question 5

altered oscillations and synchronization is observed in…

Answer 5

numerous psychiatric and neurological populations

Question 6

what are local field potentials?

Answer 6

• they are oscillations that are synchronous over a local area such as a corticol column
• can be picked up by a scalp EEG

Question 7

What do local field potentials do?

Answer 7

• the reflect the inbalance between excitation and inhibition and impact neural spiking

Question 8

What causes EEG abnormalities?

Answer 8

• excessive activity of one more brain regions
• e.g. epilepsy

Question 9

What happens during the tonic and clonic states of a grand mal seizure?

Answer 9

• tonic state causes loss of consciousness, increased muscle tone which causes stiffness (rigidity) while the clonic state is characterized by convulsions (shaking)

Question 10

describe the effects of a petite mal seizure?

Answer 10

• transient loss of consciousness
• causes you to blank out and stare
• not clear when looking at person, but spike and wave activity on EEG

Question 11

what are field potentials?

Answer 11

• collective electrical activity of a large number of distant neurons

Question 12

do EEG spike directly measure APs?

Answer 12

• No, they reflect synchronized EPSPs generated in the aligned dendrites of pyramidal cells.
• This synchronization creates the neuronal oscillations visible in EEG frequency bands (e.g., alpha, beta, delta).

Question 13

What EEG patterns are associated with wakefulness and REM sleep?

Answer 13

• it record beta (15-30 Hz) and gamma (>30Hz)
• active state/processing
• waves become less synchronized

Question 14

What EEG patterns are associated with inhibition or idling?

Answer 14

• alpha (8-14 Hz)
• person is lying awake with eyes closed
• activity decreases when person opens their eyes

Question 15

what EEG patterns are more prominent during sleep

Answer 15

• theta (4-7 Hz) oscillations are seen in sleep and modulate faster rhythms and delta (1-4 Hz) oscillations strongly expressed in deep sleep

Question 16

What happens during REM waves

Answer 16

• in REM (15-30 Hz) every 90 mins slow wave sleep changes to low voltage fast activity wave resembling beta

Question 17

When the cortex is activated which waves change activity? How did this happen?

Answer 17

• when the cortex is activated alpha (8-14Hz) activity decreases while beta (15-30 Hz) and gamma (>30 Hz) increases
• going from a state of eyes closed to eyes open

Question 18

How do you change something about perception without changing whats on the screen?

Answer 18

• to test perceptual integration use ambiguous stimuli

Question 19

What is an ambiguous stimuli? Give an example.

Answer 19

• stimuli that can be interpreted in more than one way or that is difficult to interpret at first glance
• ex. moony faces, which are black and white images that can appear as a face or be seen as a meaningless shape

Question 20

After an ambiguous stimuli is presented what do we see in an EEG?

Answer 20

• the EEG records to compare brain rhythms and synchronizations when participants reported to see a face versus when they did not
• when participants reported seeing a face you see increased gamma rhythm synchronization between electrodes

Question 21

What type of brain wave activity was seen to increase during conscious perception of ambiguous Moony faces?

Answer 21

Increased gamma (<30 Hz) integration was observed during conscious perception.

Question 22

What experimental setup was used to investigate the link between gamma activity and conscious perception of threshold visual stimuli? And what was observed?

Answer 22

• subject viewed an “at threshold” visual stimuli (a very faint image) which was seen approximately 50% of the time
• what was observed an increase in gamma activation (>30 Hz) and inter-regional synchrony when the stimuli are ‘visible’

Question 23

What type of oscillations are seen in cortical columns whose receptive fields are stimulated

Answer 23

• an increase in gamma (>30 Hz) are seen

Question 24

What happens to the gamma oscillations of cortical columns responding to a common object or stimulus?

Answer 24

• their gamma oscillations become synchronized
• this always brain to put different features of an object together in a coherent percept

Question 25

What is oscillatory coherence and why is it important?

Answer 25

- it makes sure that neurons processing related parts of a stimulus/object synchronize their gamma activity - this is important because it helps separate the object from its background, known as figure-ground segregation, and is a mechanism for feature binding, allowing you do understand your visual environment effectively

Question 26

What are the two main types of sleep we cycle through during the night, and what controls this cycling?

Answer 26

- Deep sleep and REM (dream) sleep - this is controlled by thalamic input to the cortex

Question 27

How do brain waves during wakefulness and REM sleep differ from those in deep sleep?

Answer 27

- during wakefulness and REM sleep brain waves are high frequency, low amplitude and spatially segregated (less synchronous), these are gamma and beta waves - during deep sleep wakes are low frequency, high amplitude and spatially coherent. these are delta waves

Question 28

What is the ascending reticular activating system?

Answer 28

- it is a pathway that connects the reticular formation to the thalamus and cerebral cortex. it sends cholinergic signal (ACh) to the nuclei of the thalamus, which then activates the cortex to promote wakefulness and arousal - when its activity decreases you transition towards sleep - Brainstem: nuclei in reticular formation of brain stem is the switch.

Question 29

What controls circadian rhythms

Answer 29

- the suprachiasmatic nucleus in the anterior hypothalamus, it is the 'clock' that controls circadian rhythms

Question 30

The primary function of the SCN is to act as a '24 hour clock', how is this possible?

Answer 30

- this is because genetic transcription and protein binding 'turnover' sequence which lasts 24 hours within the cells of the SCN

Question 31

What's one way to 'reset' our internal clock?

Answer 31

- when sunlight/light hits your eyes

Question 32

How does the SCN impact other organs?

Answer 32

- Since its in the hypothalamus, it links the nervous system to the hormone system, therefore SCN can influence organs via the pituitary gland (endocrine interface)

Question 33

How does the SCN influence the sleep-wakefulness cycle

Answer 33

- it does so by signalling to the ARAS beginning in the brainstem, indicating when its time to wake up

Question 34

Describe the accidental discovery found about the 24-hour sleep wakefulness cycle

Answer 34

- Context: in constant light conditions, hamsters show 24 hour sleep-wakefulness cycle, which can be tracked by wheel running - however, there was a hamster a circadian rhythm shorter than 24 hours because it had a mutation on the 'tau' gene which was critical for that 24 hour protein turnover within the SCN cells

Question 35

What is the brainstem reticular formation

Answer 35

- nuclei in the reticular formation of the brainstem is the switch to wakefulness