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.

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.

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.

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.

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 => examples from biology might be useful to CS, while CS examples and analysis useful for functional interpretation of neuroscience.

But don’t forget the neural mechanisms.

Dual rate andphase coding by place cells.

Phase relativeto EEG theta codes for position within field (O’Keefe & Recce, 1993)

Phase precession occurson low and high rate runsand in low and high rate cells, across low and highrate sections of place field

Independence of phaseand rate

Huxter, Burgess, O’Keefe, Nature in press

Firing rate codes for running speed (+trajectory,odors, reinforced stimuli)Hirase et al, Wood et al, Frank et al, Blair et al

A weak correlation of phase with rate arises from strong correln of phase with position & rate dependence on position

phase phase

xx

rate

rate

Rate of phase precession adjusts to length of field

Amount and rate of phase precession does not correlatewith field skew (r=0.13, p=0.23; r=0.09, p=0.44, n=94).