Brain Rhythms: key questions

1
Brain Rhythms key questions

• Coordination of processing across space
• Coherence in perception, e.g. synchrony
  binding,
• cognitive moment, causation/objects.
• Large-scale systems, e.g. asynchronous pulsed
  VLSI
• Dynamic connection of sub-processors, e.g.
  synchrony between brain regions (perception,
  memory retrieval)?
• Coordination of processing across time
• Clocking/chunking time for perception memory
• Organising/storing order of segments
• Using phase within clock cycles, e.g. phase
  coding in olfactory bulb and hippocampus.

2
Brain Rhythms key questions

• Combining temporal and rate codes
• Rhythms part of Rosetta stone of neural code?
• Temporal augments rate, e.g. coordination in
  space time
• Temporal and rate parallel independent (immense
  power, harder to coordinate?), e.g. hpc phase
  code for location, rate code for speed,
  trajectory, objects.
• Learning/adaption
• Find equivalent to rate-learning by synaptic
  modification, e.g. experience-dependent
  modification of frequencies or dynamics
  (olfactory cortex?).
• Interaction with synaptic modification rate and
  temporal pattern dependence parallel or
  interacting use of same synapses?
• Hard / software analogues/ implementation.

3
Brain Rhythms key questions

• Are rhythms themselves important?
• Important indicator/side-effect of basic
  mechanisms
• BUT not causal themselves.
• Computational models important we do have
  direct effects of synch./oscillations to neural
  firing, transmission, synaptic modification.
  These can be causal.
• V. important to investigate the
  BEHAVIOURAL/cognitive problems and the NEURAL
  mechanisms involved.
• Technological advance in large-scale single-unit
  recording at least as important as advances in
  monitoring oscillations.

4
Brain Rhythms key questions

• Useful analogies for artificial systems?
• We can use time-stamps and global clocks already
  perhaps this motivates synchrony of rhythms in
  diverse areas phase coding in brain provides
  efficient time-stamp if common rhythm is present.
• Availability of massive memory and processing
  capability/ coordination of large-scale connected
  systems (inc WWW), excitable media might require
  creative brain-inspired solutions.

5
Brain Rhythms prospects

• Recent progress/new questions in both
  neuroscience re. use of rhythms and temporal
  processing, possibly needed in future
  hard/software .
• Links between synapses, single units, EEG BOLD
  with behavior availability of massive memory and
  processing capability/ coordination of
  large-scale connected systems (inc WWW).
• Novelty of field and wide potential implications
  gt examples from biology might be useful to CS,
  while CS examples and analysis useful for
  functional interpretation of neuroscience.
• But dont forget the neural mechanisms.

6
Dual rate and phase coding by place cells.
Phase relative to EEG theta codes for position
within field (OKeefe Recce, 1993)
7
Independence of phase and rate
Huxter, Burgess, OKeefe, Nature in press
Phase precession occurs on low and high rate
runs and in low and high rate cells, across low
and high rate sections of place field
Firing rate codes for running speed
(trajectory, odors, reinforced stimuli) Hirase
et al, Wood et al, Frank et al, Blair et al
8
A weak correlation of phase with rate arises from
strong correln of phase with position rate
dependence on position
phase
phase
rate
rate
x
x
9
Rate of phase precession adjusts to length of
field
10
Amount and rate of phase precession does not
correlate with field skew (r0.13, p0.23
r0.09, p0.44, n94).