Unveiling the neural code
Sensory stimuli are received, processed and transformed into motor commands. How these commands are coded and communicated in such brief response times and with such accuracy still remains unclear.One of the theories proposed to explain neuronal information transmission is based on the Winner-Take-All (WTA) approach. It is theorised that spiking neurons are trained to respond to repeated sequences of sensory cues. As a result, they induce ordered patterns of neuronal activity that consist of a brief steady state followed by sharp neuronal transitions. The EU-funded ′Winner-Take-All readout mechanisms in the central nervous system′ (WTAINCNS) project set out to study the accuracy of a temporal WTA framework for the neural response to a stimulus. Researchers suggested a latency-based competitive mechanism to explain transmission of the external stimulus based on the identity of the neuron that fired the first spike in the population.To this end, they used a mathematical model to analyse important parameters in neural transmission and determine how they affect WTA accuracy. Their theoretical investigation was combined with experimental data from different systems. In particular, the model was used to study the early visual system in the fish and the monkey, as well as determine sound source localisation in the guinea pig. Results showed that cells responsible for sound source localisation achieve interaural time delay (ITD) by regulating the rate at which they fire the particular signal. ITD is the difference in sound arrival time between the two ears. The mechanism they use essentially takes into account the total number of spikes fired by the cell in the entire neural response to the auditory stimulus. The WTAINCNS computational approach provides a useful tool for studying neuronal responses and deciphering the response latency observed in both the auditory and visual systems. In the long run, this information could be exploited in brain-computer interface neuroprosthetics' applications that aim to restore damaged hearing, sight and movement.
Keywords
Neuronal code, Winner-Take-All approach, interaural time delay, mathematical model
