Oscillations, synchrony and temporal codes in cortical processing

In principle, neurons can encode information in at least two ways , i) by varying the amplitude of their response (rate code) and/or ii) by adjusting the precise timing of individual discharges (temporal code). It is proposed that cortical networks use both coding strategies in parallel, exploiting their respective advantages. Evidence is presented that precise coordination of spike timing across neuronal assemblies is frequently associated with an oscillatory patterning of discharge sequences in the beta and gamma frequency range and the synchronisation of distributed responses with millisecond precision. This synchronisation appears to be exploited to i) jointly raise the saliency of responses to sensory stimuli in the context of perceptual grouping (binding), ii) read out grouping criteria residing in the functional architecture of cortical networks during the free exploration of visual scenes , iii) prepare as a function of attention and response anticipation the hand-shaking between distributed cortical regions , iv) determine the occurrence and polarity of use dependent synaptic modifications and v) gate the access of sensory signals to consciousness. Recent data indicate further that cognitive functions requiring dynamic binding are disturbed in schizophrenia patients and that these deficits go along with a reduced ability to precisely synchronize responses across distributed cortical networks. The possibility is suggested that some of the dissociative symptoms characteristic of this disease result from impaired binding functions.