Download The mechanism of the alpha rhythm

By Annemari de Silva
Supervised by Prof. Peter Robinson
Corticothalamic Model:
A Simple Model to explain the Alpha Rhythm
 EEG: measures electrical activity
α rhythm
of brain.
 Driving Questions:
 Why this behaviour at ~10Hz?
 Is there a simple model to describe it?
 What mainly contributes to it?
 Different explanatory models
 Our simplified model –
Corticothalamic Resonance
CORTEX
Fig 1. Power Spectrum from EEG (electroencephalogram)
Fig 1. Robinson, P.A. et al. Multiscale brain Modelling 2005
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THALAMUS
Mechanism of Resonance
CORTEX
(e)
‘Spreading
out’
term
Gee – Gain from
activity in cortex
Gese – Gain from
cortex-thalamus travel
THALAMUS (s)
Gesn – Gain from
incoming signals
sensory neurons (n)
Mathematical Model:
Transfer Function, q2 and Power Spectrum.
Frequency (Hz)
•Using mathematical
model, vary parameters
•Observe effects on graphs
and find physiological
correspondence
Frequency (Hz)
Varying t0 (time delay for cortex-thalamus travel)
t0 low
Real (q2)
Fig 5: a) Imaginary (q2) vs. Real (q2)
Frequency (Hz)
b) Power vs. Frequency
t0 high
Real (q2)
Fig 6: a) Imaginary (q2) vs. Real (q2)
Frequency (Hz)
b) Power vs. Frequency
Varying gamma, alpha and gains
 high
Damping
term
‘Spreading
out’
term
 low
Gee – Gain from activity in cortex
Gese – Gain from cortex-thalamus
Frequency (Hz)
Fig 1. Power Spectrum – GAMMA
varied
travel
Gese high
Gee low
 high
 low
Frequency (Hz)
Fig 2. Power Spectrum – ALPHA
varied
G
 ese low
Gee high
Frequency (Hz)
Fig 3. Power Spectrum – GAINS
varied
Overview
What causes alpha rhythm?

 Resonance effect between cortex and
thalamus.
 Many physical factors involved in total
time delay and amplitude in feedback
mechanism.
 How good is corticothalamic model?
 Very! Look at graph!
Our version is simplified to get basic gist
of contribution of parameters.
 Efficiency in explaining most aspects
of EEG power spectrum
 Maths corresponds to physiology
 Simplicity of model
•
Relevance to other fields.
 Local vs global connections