Lecture 32 Flashcards
Explain the importance of synchronization in neuronal communication
- boosts information transfer between brain regions or columns
- Oscillations 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 neuron’s response to input and likelihood of spike production
Neurons in sync are considered phase-locked
What are local field potentials?
Oscillations that are synchronous over a local area such as a cortical column. Can be picked up by scalp EEG
Draw an EEG consistent with tonic and clonic states of a grand mal seizure. Define the tonic and clonic states of a grand mal seizure
Tonic seizures cause a stiffening of muscles while clonic seizures are characterized by jerking or twitching.
Draw an EEG consistent with a petite mal seizure
transient loss of consciousness
An absence seizure causes you to blank out or stare into space for a few seconds.
EEG looks like cursive ns linked together. smooth waves
Define EEGs and explain different EEG patterns associated with different states of wakefulness
EEG: electroencephalography
Beta (15-30Hz) and gamma (>30Hz) oscillations seen only in wakefulness; reflect active state/prcoessing
alpha (8-14 Hz): oscillations reflect inhibition or idling
theta (4-7 Hz): oscillations
are associated with
modulating faster rhythms,
also seen in sleep
delta (1-4 Hz): oscillations strongly expressed in sleep
REM (15-30 Hz): every ~90
min slow wave sleep
changes to low-voltage fast
activity wave resembling beta
Deep sleep is low-frequency, high amplitude, spatially coherent
Wakefulness and REM are high-frequency, low amplitude and
spatially segregated (less synchronous)
Bats Drink Blood, which stands for Beta, Alpha, Theta, and Delta waves. This order reflects the decreasing frequency and increasing amplitude of brainwaves as a person moves from alert wakefulness to deep sleep (excl. rem)
Explain what is observed with MEG in the V1 cortex when the eyes are open vs closed
V1 cortex, when eyes are open, relative to eyes closed, more gamma, more beta, less alpha (10hz) waves
In general, when a specific cortical area is ‘activated’, alpha (8-14 Hz) activity decreases and an increase in beta (15-30 Hz) and gamma (>30 Hz)
Explain the moony faces experiment
ambiguous stimuli (moony faces) presented to subject. Participant presses button to indicate if they saw a face or not. EEG is recorded to compare brain rhythms and synchronization.
Increased gamma (<30Hz) integration during conscious perception (when they could see something coherent as opposed to meaningless). activity in certain electrodes were synchronized (phase locked)
- regions phase locked: prefrontal cortex, visual cortex, inferior temporal cortex, medial temporal lobe (recognition of faces)
Difference between cortical columns and broadmann areas
Cortical columns are small areas of 6-layer cortex with the same receptive field
Brodmann areas are large areas of cortex with homogenous 6-layer cytoarchitecture
Structurally defined Brodmann areas tend to be associated with specific functions
Motor, perceptual and cognitive processes requires selective integration between
particular groups of columns located in particular Brodmann areas
Explain the following structures in the brain
- suprachiasmatic nucelus
- brainstem reticular formation
- ascending reticular activating system
suprachiasmatic nucleus in the anterior hypothalamus contains a 24 hour clock controlled by a gene-turnover cycle. sends signals to the brainstem reticular formation to impact sleep-wakefullness cycle. also influences other organs through the pituitary (endocrine interface)
- external stimuli such as light can affect the internal clock
Brainstem: nuclei in reticular formation of brain stem is the switch.
ascending reticular activating system is the pathway that connects the reticular formation to the thalamus and cerebral cortex. Sends cholinergic signals (acetylcholine) to the nuclei of the thalamus, which then activate the cortex.
As the ARAS activity declines, it allows sleep centers to take over, leading to the transition from wakefulness to sleep.
Explain jet lag
Jet-lag: internal clock does not match the outside stimuli (light-darkness cycle)
Sunlight on the retina resets this progress but it takes time
What is a tau mutant hamster
Even in constant light conditions, hamsters show 24 hour sleep- wakefulness cycle, which can be tracked by wheel running
Discovered hamsters with a spontaneous circadian rhythms shorter than 24 hours
Cause is a mutation on the ‘tau’ gene involved with ‘turnover cycle’ in the
‘circadian clock’ within the suprachiasmatic nucleus
What is the importance of phase-locking during neural oscillations?
- Signal boosts, affecting the likelihood of spike output and sensitivity to synaptic input
- Increases communication between different areas
- By synchronizing neurons coding for the same object, phase-locking helps the brain separate figures from background — a process known as figure-ground segregation.
