Neuronal activity and sensory encoding
Depolarisation or hyperpolarisation of the resting membrane potential or spike activity that happens when a depolarisation threshold is crossed are measures of neuronal activity. Electrical activity can be recorded in single neurons or populations (a field potential average). Individual cortical neurons have also been shown to switch spontaneously between an up state (slightly depolarised) and a down state (hyperpolarised). These fluctuations are more conspicuous during synchronised slow-wave oscillations recorded from populations of cells, and the two are thought to be related. Scientists investigated the stochastic nature of cortical networks with EU funding of the NETDYNCORTEX (Network dynamics of auditory cortex and the impact of correlations on the encoding of sensory information) project. Animals under urethane anaesthesia exhibit patterns of cortical activity similar to those seen in non-anaesthetised animals. Scientists studied the periods of up and down activity in auditory cortex of anaesthetised rats during activity similar to that of slow-wave sleep. The periods were more irregular than previously thought, suggesting the two phenomena may not be related. Computational network models pointed to possible mechanisms of up and down activity and functions. The team then studied pair-wise noise correlations, a phenomenon by which two nearby cells tend to share a part of the statistical variability in their spiking patterns. Interestingly, scientists showed that the correlations were primarily due to periods during which all neurons have no spiking activity, in contrast to previous studies arguing the correlations are due to shared anatomical input. A model confirmed that possibility. A computational model coupling a standard sensory circuit to a standard decision-making circuit was used to make predictions about the role of neuronal fluctuations on perceptual decision making. The model explained an important contradiction in the literature and predictions were confirmed in recordings from monkeys. Additional studies investigated the role of recent experience on predictions of likely stimuli in rats performing an auditory discrimination task. NETDYNCORTEX highlighted the complexity of the relationship between stochastic non-linear dynamics present in cortical circuits, underlying mechanisms and perception. The data have shed light on potential cortical mechanisms of information processing and establish tools for further investigation.
Keywords
Neuronal activity, sensory encoding, cortical networks, auditory cortex, sensory information
