Neural Coding: Oscillations Help to Decode Spike Patterns

ReseaRch highlights

the Journal of Neuroscience, they that the downstream neuron learned NEURAL CODING report that PoFC aids spike timing- to decode the spiking pattern. dependent plasticity (STDP) and, When the authors did not reset Oscillations help to thus, neural coding and decoding. the input neurons but instead STDP is a learning rule according introduced an oscillatory drive, the decode spike patterns to which synaptic strength is input currents automatically became modified as a function of the rela- encoded in the spike phases with tive timing of pre- and postsynaptic respect to the oscillation (PoFC). spikes; it allows neurons to respond As a result, the downstream STDP selectively to repeating spike patterns neuron received input in the form of in continuous spike trains. Here, the ‘spike waves’, which were even more authors show that oscillatory activity efficiently detected than in the reset- facilitates this information decoding. ting paradigm and which triggered Using computer simulations, they a learned selective response. These investigated the mechanisms through responses were observed even when which a single neuron capable of only a small fraction of the afferents undergoing STDP can detect and (~10%) exhibited PoFC. learn to selectively respond to pat- Both theoretical and experimental terns of input from an unknown studies have provided evidence that number of afferents occurring at oscillatory activity improves the reli- unpredictable times. ability of neuronal spike timing, but The downstream neuron was the functional consequences of this unable to learn the repeating patterns were unknown. This study shows that In sensory processing, a neuron’s when Poisson input neurons (in oscillations facilitate downstream firing rate and the timing of the spikes which the spiking probability at any processing by generating waves of relative to the stimulus onset together instant is constant and independent spikes with reliable relative times that encode information. In reality, of prior activity) or independent the downstream neuron can decode. however, stimuli are often ongoing, leaky integrate-and-fire (LIF) input As a result, these neurons can raising the question of what else could neurons (with piecewise constant respond selectively to spike patterns provide a reference point for spike input currents) were used. However, and, importantly, learn to respond to timing. Previous studies suggested when the authors occasionally reset these patterns. Together, these find- that the phase of ongoing background the membrane potential of all LIF ings suggest that oscillatory activity oscillations in the local field potential input neurons (which might be might have a major role in long-term might provide this reference point. similar to what happens in the brain memory encoding. The timing of spikes relative to the during saccades in vision or sniffs Monica Hoyos Flight phase of an oscillation has been in olfaction), the downstream STDP ORIGINAL RESEARCH PAPER Masquelier, T., referred to as ‘phase-of-firing coding’ neuron began to respond to repeated Hugues, E., Deco, G. & Thorpe, S. J. Oscillations, (PoFC). Masquelier et al. now show spiking patterns. The selectivity of phase-of-firing coding, and spike timing- dependent plasticity: an efficient learning that PoFC indeed has a functional this response emerged after several scheme. J. Neurosci. 29, 13484–13493 (2009) role in information processing. In stimulations and resets, indicating