Most natural actions are chosen voluntarily from many possible choices. An action is often chosen based on the reward that it is expected to produce. What kind of cellular activity in which area of the cerebral cortex is involved in selecting an action according to the expected reward value? Results of an analysis in monkeys of cellular activity during the performance of reward-based motor selection and the effects of chemical inactivation are presented. We suggest that cells in the rostral cingulate motor area, one of the higher order motor areas in the cortex, play a part in processing the reward information for motor selection.

To achieve a volitional goal, we need to execute multiple movements in a specific temporal order. After repetitive performance of a particular sequence of movements, we are able to memorize and execute the whole sequence without external guidance. Where and how in the brain do we store information necessary for the orderly performance of multiple movements? We have found a group of cells in the cerebral cortex of monkeys whose activity is exclusively related to a sequence of multiple movements performed in a particular order. Such cellular activity exists in the supplementary motor area, but not in the primary motor cortex. We propose that these cells contribute a signal about the order of forthcoming multiple movements, and are useful for planning and coding of several movements ahead.

To study how neurons in the medial motor areas participate in performing sequential multiple movements that are individually separated in time, we analyzed neuronal activity in the supplementary (SMA) and presupplementary (pre-SMA) motor areas. Monkeys were trained to perform three different movements separated by waiting times, in four or six different orders. Initially each series of movements was learned during five trials guided by visual signals that indicated the correct movements. The monkeys subsequently executed the three movements in the memorized order without the visual signals. Three types of neuronal activity were of particular interest; these appeared to be crucially involved in sequencing the multiple motor tasks in different orders. First, we found activity changes that were selective for a particular sequence of the three movements that the monkeys were prepared to perform. The sequence-selective activity ceased when the monkeys initiated the first movement. Second, we found interval-selective activity that appeared in the interval between one particular movement and the next. Third, we found neuronal activity representing the rank order of three movements arranged chronologically; that is, the activity differed selectively in the process of preparing the first, second, or third movements in individual trials. The interval-selective activity was more prevalent in the SMA, whereas the rank-order selective activity was more frequently recorded in the pre-SMA. These results suggest how neurons in the SMA and pre-SMA are involved in sequencing multiple movements over time.

Interval timing is an essential guiding force of behavior. Previous reports have implicated the prefrontal and parietal cortex as being involved in time perception and in temporal decision making. We found that neurons in the medial motor areas, in particular the presupplementary motor area, participate in interval timing in the range of seconds. Monkeys were trained to perform an interval-generation task that required them to determine waiting periods of three different durations. Neuronal activity contributed to the process of retrieving time instructions from visual cues, signaled the initiation of action in a time-selective manner, and developed activity to represent the passage of time. These results specify how medial motor areas take part in initiating actions on the basis of self-generated time estimates.

It has been empirically established that the cerebral cortical areas defined by Brodmann one hundred years ago solely on the basis of cellular organization are closely correlated to their function, such as sensation, association, and motion. Cytoarchitectonically distinct cortical areas have different densities and types of neurons. Thus, signaling patterns may also vary among cytoarchitectonically unique cortical areas. To examine how neuronal signaling patterns are related to innate cortical functions, we detected intrinsic features of cortical firing by devising a metric that efficiently isolates non-Poisson irregular characteristics, independent of spike rate fluctuations that are caused extrinsically by ever-changing behavioral conditions. Using the new metric, we analyzed spike trains from over 1,000 neurons in 15 cortical areas sampled by eight independent neurophysiological laboratories. Analysis of firing-pattern dissimilarities across cortical areas revealed a gradient of firing regularity that corresponded closely to the functional category of the cortical area; neuronal spiking patterns are regular in motor areas, random in the visual areas, and bursty in the prefrontal area. Thus, signaling patterns may play an important role in function-specific cerebral cortical computation.

Spike sequences recorded from four cortical areas of an awake behaving monkey were examined to explore characteristics that vary among neurons. We found that a measure of the local variation of interspike intervals, L(V), is nearly the same for every spike sequence for any given neuron, while it varies significantly among neurons. The distributions of L(V) values for neuron ensembles in three of the four areas were found to be distinctly bimodal. Two groups of neurons classified according to the spiking irregularity exhibit different responses to the same stimulus. This suggests that neurons in each area can be classified into different groups possessing unique spiking statistics and corresponding functional properties.

Both supplementary and presupplementary motor areas are crucial for the temporal organization of multiple movements. J. Neurophysiol. 80: 3247-3260, 1998. To study the involvement of the supplementary (SMA) and presupplementary (pre-SMA) motor areas in performing sequential multiple movements that are individually separated in time, we injected muscimol, a gamma-aminobutyric acid agonist, bilaterally into the part of each area that represents the forelimb. Two monkeys were trained to perform three different movements, separated by a waiting time, in four or six different orders. First, each series of movements was learned during five trials guided by visual signals that indicated the correct movements. The monkeys subsequently executed the three movements in the memorized order, without the visual signals. After the injection of muscimol (3 microliter, 5 micrograms/microliters in 10 min) into either the SMA or pre-SMA bilaterally, the animals started making errors in performing the sequence of movements correctly from memory. However, when guided with a visual signal, they could select and perform the three movements correctly. The impaired memory-based sequencing of movements worsened progressively with time until the animals could not perform the task. Yet they still could associate the visual signals with the different movements at that stage. In control experiments on two separate monkeys, we found that injections of the same amount of muscimol into either the SMA or pre-SMA did not cause problems with nonsequential reaching movement regardless of whether it was visually triggered or self-initiated. These results support the view that both the SMA and pre-SMA are crucially involved in sequencing multiple movements over time.

The anterior part of the parietal association area in the cerebral cortex of primates has been implicated in the integration of somatosensory signals, which generate neural images of body parts and apposed objects and provide signals for sensorial guidance of movements. Here we show that this area is active in primates performing numerically based behavioural tasks. We required monkeys to select and perform movement A five times, switch to movement B for five repetitions, and return to movement A, in a cyclical fashion. Cellular activity in the superior parietal lobule reflected the number of self-movement executions. For the most part, the number-selective activity was also specific for the type of movement. This type of numerical representation of self-action was seen less often in the inferior parietal lobule, and rarely in the primary somatosensory cortex. Such activity in the superior parietal lobule is useful for processing numerical information, which is necessary to provide a foundation for the forthcoming motor selection.