In the early 20th century, sensing was typically considered passive. The prevailing notion was that the nervous system processed sensory inputs without playing an active role in modulating the signals. Around 1950, R. W. Sperry as well as E. von Holst and H. Mittelstaedt proposed that self-generated neural activity, which was labeled "reafference" by von Holst and Mittelstaedt, is also important in sensory processing. Over the years, the notion that sensing is an active process, with self-generated “efference copy” processed alongside sensory inflow, has been demonstrated across a broad range of sensory systems in a wide variety of species (e.g., insects, bats, rats, and humans). This Collection from the Journal of Neurophysiology is focused on how self-generated neural activity influences the processing of sensory information. (Image: http://dx.doi.org/10.1152/jn.00657.2015)
Cover: Electrophysiological and morphological measurements were obtained simultaneously from a single corticospinal neuron. These data served as constraints on evolutionary optimization, generating a family of corticospinal models. A three-dimensional reconstruction serves as the backbone for a pseudo-color visualization of synaptic efficiency as a function of dendritic location, simulated in a single biophysical model selected from the family of optimal individuals. Excitatory synapses at yellow dendritic locations resulted in the largest depolarizations at the soma, while the same synaptic activation at purple locations generated only weak somatic depolarizations. This visualization is surrounded by scatter plots representing the evolutionary optimization: biophysical models optimized across different fitness functions demonstrate tradeoffs between full high-dimensional error (y-axis) and individual error scores (individual x-axes; clockwise order from top
left: subthreshold error, instantaneous firing rate error, spike-shape error, average firing rate error). Color based on 5 error percentiles in increasing instantaneous firing-rate error (purple, red, dark orange, light orange, yellow). From Neymotin SA, Suter BA, Dura-Bernal S, Shepherd GMG, Migliore M, Lytton WW. Optimizing computer models of corticospinal neurons to replicate in vitro dynamics. J Neurophysiol; doi:10.1152/jn.00570.2016.