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Publisher Summary This chapter discusses population coding in the motor cortex. Single unit activity, accounted for input-output transforms in distributed neural networks. Serial recording during a stereotyped task has no demerits in understanding population coding, assuming a reasonable neuronal sample, and a hypothesis related to relatively stereotyped input-output mappings. Complex, emergent features of neuronal ensembles is not needed for an understanding of input-output mappings, but may play a role in more fundamental information-processing functions, such as learning, coordination among parallel networks, and attention to action. The population vector is computed from the activity of hidden units, but its accuracy does not depend on direct influences of hidden units on output elements. Cosine-like tuning and population vector coding emerged from a minimal-assumption network. The population vector rotated when the input output function is changed from the standard mapping to a nonstandard one. Population-vector rotation is accounted by a transition between two inputs, one representing the visual signal and reflecting standard visuomotor mapping, and the target signal into which it is transformed, and reflecting nonstandard mapping. The changes of hidden-unit tuning properties that occurred while the network learned a nonstandard transform corresponded to those observed in the motor cortex of a monkey that learned analogous transforms. The tuning properties of individual cells changed during the learning of both transformational and arbitrary mappings. During learning, the population vector became more accurate in both model and biological networks, for both standard and nonstandard mappings, and for both transformational and arbitrary nonstandard mappings.

Publisher Summary Several recent reports have shown that the primate premotor cortex is a distinct cortical field that plays a specialized role in the cerebral control of movement. However, the definition of the premotor cortex has been the source of difficulty, and as the premotor cortex is currently defined, its role in motor control has been questioned seriously. It must be emphasized, however, that not all neurons in the premotor cortex are movement related. Some cells appear to be responsive to the sensory signals that guide movement, others appear to reflect the animal's preparation for movement based on such sensory cues, and still others appear to be modulated in anticipation of predictable environmental events or stimuli. For heuristic purposes, these patterns have been termed “signal-related,” “set-related,” and “anticipatory,” respectively. These activity patterns are not mutually exclusive— that is, they are often combined in individual cells. Two observations reported in this chapter support the proposition that these changes are functionally related to the limb movement, rather than any concomitant sensory stimulus: (1) the changes of neuronal activity are more closely time-locked to the beginning of the movement than to the visuospatial cues that trigger the movement, and (2) neuronal modulations occur when the limb is moved “spontaneously” in total darkness.