Kiyoshi Kurata

Premotor cortex of rhesus monkeys : set-related activity during two conditional motor tasks

SummaryWe compared set-related premotor cortex activity in two conditional motor tasks. In both tasks, a rhesus monkey moved its forelimb to one of two possible targets on the basis of visuospatial instruction stimuli. One target was located to the left of the limbs starting position, the other to the right. In the directional task, a white light situated within the target provided the instruction. In the arbitrary task, colored instruction stimuli equidistant from the targets established an arbitrary relationship between stimulus and response. One hypothesis about setrelated premotor cortex activity is that it contributes to the preparation for limb movement on the basis of sensory instruction stimuli. If set-related activity differed profoundly in the arbitrary and directional tasks, then that hypothesis would be untenable. Out of 403 task-related premotor cortex neurons in two monkeys, 130 neurons showed set-related activity, and we studied 118 cells in detail. The vast majority (81%) of these 118 neurons showed no significant difference between the two tasks in set-related activity. When set-related activity did differ, the greatest activity usually occurred after arbitrary instructions; the opposite being the case for only 5% of our sample. Differences in activity during the two tasks, even when statistically significant, were generally small. The present results accord with the hypothesis that set-related premotor cortex activity reflects aspects of motor preparation.

Corticocortical inputs to the dorsal and ventral aspects of the premotor cortex of macaque monkeys

Recent cytoarchitectonic, histochemical and physiological studies have shown that the lateral part of area 6 (the premotor cortex) of macaque monkeys can be divided into at least two subregions, each of which is considered to play an important role in motor control. One lies in the dorsal aspect of the premotor cortex (PMd) medial to the spur of the arcuate sulcus, and the other in the ventral aspect of the premotor cortex (PMv) lateral to it. Since there is little information on the corticocortical inputs to the PMd, wheat-germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) was injected into both the PMd and PMv to study corticocortical inputs to these two regions, and the distribution of retrogradely labeled cells was compared. When WGA-HRP was injected into the region immediately lateral to the superior precentral sulcus within the PMd, retrogradely labeled neurons were found in area 6 lying in the mesial wall possibly corresponding to the supplementary motor area (SMA), areas 24 and 23 of the cingulate cortex, rostral region of area 4, and area 5 (area PEa). In contrast, when WGA-HRP was injected into the PMv immediately caudal to the arcuate sulcus and lateral to the spur of the arcuate sulcus, the labeled cells were found in area 7 (areas POa, PF, PFG), area 5 (area PEa), area PFop (secondary somatosensory area), SMA, the cingulate cortex (areas 24), caudal region of area 4 in the rostral bank of the central sulcus, and area 3a. It appears that the differences in the corticocortical inputs contribute to specialization of the PMd and PMv for their differential roles in motor control.

The relationship between salivary biomarkers and state-trait anxiety inventory score under mental arithmetic stress: a pilot study.

Measurement of stress hormones is a common objective method for assessment of mental stress. However, the stress of blood sampling alone may also increase stress hormone levels. In the present study, we sampled salivary biomarkers from healthy volunteers under noninvasive conditions and determined their efficacy to assess mental stress. Specifically, we examined the relationship between State Anxiety Inventory score (STAI-s) in subjects exposed to arithmetic stress and salivary chromogranin-A, &agr;-amylase, or cortisol. The STAI-s was significantly correlated to salivary &agr;-amylase (r = 0.589; P < 0.01) but not to salivary chromogranin-A or cortisol. Therefore, salivary &agr;-amylase is a useful indicator of psychosocial stress.

Premotor and supplementary motor cortex in rhesus monkeys: neuronal activity during externally- and internally-instructed motor tasks

SummaryWe compared neuronal activity in the premotor (PM) and supplementary motor cortex (SM) of two rhesus monkeys as they performed two tasks. In an externally-instructed task, a visuospatial instruction stimulus indicated which of two touch pads should be the target of a forelimb movement. In an internally-instructed task, the visuospatial stimulus was either irrelevant or not presented, but in either case the target alternated between the two touch pads in blocks of 20 trials each. In both tasks, the monkey withheld movement for a self-timed delay period. Neuronal activity modulation during the delay period (set-related activity) and immediately before movement (movement-related activity) was comparable in PM and SM, both in terms of the proportion of cells with both of those activity patterns and their depth of modulation. Thus, our findings do not provide strong support for a clear-cut functional division between PM and SM regarding the control of externally- and internally-instructed limb movements. Within PM, 57 out of 96 cells with set-related activity showed similar modulation during the two tasks, supporting the proposition that such activity contributes to the preparation for a limb movement. In 32 of the 39 PM set-related neurons that showed a significant activity difference between the two tasks, activity was greater in the externally-instructed task. This finding supports the hypothesis that set-related activity in PM contributes more to sensorially-instructed than to other movements.

Information processing for motor control in primate premotor cortex

Recent neurophysiological as well as neuropsychological studies provided evidences on how various informations are processed to generate motor programs in the central nervous system. In this article, functional specializations of two distinct cortical motor areas, the dorsal and ventral aspects of the premotor cortex (PMd and PMv, respectively) of macaque monkeys, are focused to review this issue. Three major conclusions emerged from recent neurophysiological studies. First, each of movement parameters such as amplitude and direction is distinctively programmed in PMd by serial integration, rather than by parallel distributed processing. Second, in performance of conditional motor behavior, conditionally presented sensory signals are processed for motor preparation and execution of an intended act in PMd, but not in PMv. Third, PMv may be specialized for motor execution under visual guidance.

Relating Neuronal Firing Patterns to Functional Differentiation of Cerebral Cortex

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.

Distribution of neurons with set- and movement-related activity before hand and foot movements in the premotor cortex of rhesus monkeys.

SummaryNeuronal activity was studied in the premotor cortex (PM) of two rhesus monkeys, each of which performed both forelimb and hindlimb movements. On each trial, the monkey received a visual instruction stimulus (IS) that indicated whether a foot or a hand movement would be rewarded on that trial. After a delay period, during which the monkey withheld an overt movement, a visual trigger stimulus (TS) was presented to indicate that the monkey should execute a movement. Of 572 task-related neurons recorded in PM, 149 neurons showed set-related activity, defined as a significant increase or decrease in discharge rate throughout most of the instructed delay period, and 299 neurons showed movement-related activity, defined as a significant change in discharge rate between the TS and movement onset. Both setand movement-related activity were subdivided into three patterns: activity modulation 1) before a foot movement only (“foot” neurons); 2) before a hand movement only (“hand” neurons); and 3) before both foot and hand movements (“mixed” neurons). The distribution of set-related neurons mostly overlapped with that of movement-related neurons, although set-related neurons were located in more restricted regions than movement-related neurons. “Foot” neurons with setand movementrelated activity were distributed near the superior precentral sulcus. “Hand” neurons were mainly located lateral to the “foot“ neurons with some overlap. The results indicate that most PM setand movement-related neurons contribute, respectively, to the preparation for and execution of specific limb movements, as opposed to movement per se. Further, the differential distribution of neurons with activity related to hindlimb vs. forelimb movement supports previous indications that PM is topographically organized.

Neuronal activity in the cortical supplementary motor area related with distal and proximal forelimb movements

Monkeys were trained to perform two different motor acts, one involving muscle activity in distal forelimb muscles and the other in proximal forelimb and shoulder girdle muscles. After confirming spatial and temporal dissociation of muscle activity in the two motor acts, single unit activity in the supplementary motor area (SMA) was recorded. SMA neurons related with the distal and proximal forelimb movements were found to be arranged rostrocaudally with a considerable overlap. In the overlapping region, neurons related with the distal movement were located more deeply.

Changing concepts of motor areas of the cerebral cortex

Recent development of studies on cerebral cortex of primates provides evidence that there exist multiple motor representation areas in the frontal lobe. By analyzing the activity of single cells in association with performance of a variety of motor behavior, new concepts on the functional role of each area are developing.

Site of origin of projections from the thalamus to dorsal versus ventral aspects of the premotor cortex of monkeys

Retrograde tracers were injected into the forelimb regions of three cortical motor areas: (1) a dorsal aspect of the premotor cortex (PMd) immediately lateral to the superior precentral sulcus; (2) a ventral aspect of the premotor cortex (PMv) immediately caudal to the genu of the arcuate sulcus and lateral to the arcuate spur; and (3) the primary motor cortex (MI). Before tracer injection, single-unit recordings were made to select injection sites in the forelimb regions where neurons with set- and/or movement-related activity before forelimb movements were densely located. Following the PMd injections, labeled cells were found mainly in rostral portion of VLc and VLo. Cells projecting to PMv were found mainly in X and VPLo. Projection cells to the MI were found in VPLo, VLc, and VLo. Locations of neurons projecting to different motor areas were not overlapped in the thalamic nuclei. Combining available reports, the results suggest that major inputs to PMd come from globus pallidus and that, in contrast, cerebellum is a main source to the PMv. The differential inputs to PMd and PMv may contribute to their functional specialization.