Arcuate Sulcus Research Articles

Motivation-dependent activity in the dorsolateral part of the prefrontal cortex in the monkey

Field potentials were recorded on self-paced hand and mouth movements with implanted electrodes on the surface and at 2.0–3.0 mm depth in respective cortical areas in seven monkeys. Surface-negative (s-N), depth-positive (d-P) premovement slow potentials were recorded in the prefrontal cortex only when the movements were performed with an intense motivation for a reward. Such a motivation-dependent activity was mainly obtained in the rostral bank of the arcuate sulcus on both sides (except for the inferior limb of the arcuate sulcus in the left hemisphere). Three of the seven monkeys were also tasked with visuo-initiated hand movements. As motivation for reward decreased, s-N, d-P potentials at a latency of about 80 ms after stimulus onset became gradually smaller in the rostral bank of the arcuate sulcus in the right hemisphere. These facts suggest that motivation-dependent activity is represented in the dorsolateral part of the prefrontal cortex in monkeys, and that the cortical part is involved in motivational functions as well as in cognitive functions.

1527 Comparison between neural organization from the superior colliculus to horizontal and vertical ocular motoneurons

Injections of the retrograde tracer [125I]wheat germ agglutinin have been placed in different areas of the paramedian pontine reticular formation (PPRF), a well known premotor center for gaze control. Experiments in 5 monkeys revealed 3 major sources of input: (1) bilateral projections from the so-called frontal eye field (FEF), which is situated in the frontal cortex around the arcuate sulcus; (2) the intermediate and deep layers of mainly the contralateral superior colliculus; and (3) ipsilateral projections from brainstem structures such as the accessory oculomotor nuclei (nucleus interstitialis of Cajal, nucleus of Darkschewitsch, and nucleus of the posterior commissure), the mesencephalic reticular formation, the vestibular nuclei, the nucleus prepositus hypoglossi, and the cerebellar fastigial nucleus. The results are compared with previous anatomical investigations and confirm the electrophysiologically demonstrated FEF-PPRF-abducens disynaptic pathway.

1525 Measurement of vestibulo-ocular reflex and optokinetic response in the mouse

Injections of the retrograde tracer [125I]wheat germ agglutinin have been placed in different areas of the paramedian pontine reticular formation (PPRF), a well known premotor center for gaze control. Experiments in 5 monkeys revealed 3 major sources of input: (1) bilateral projections from the so-called frontal eye field (FEF), which is situated in the frontal cortex around the arcuate sulcus; (2) the intermediate and deep layers of mainly the contralateral superior colliculus; and (3) ipsilateral projections from brainstem structures such as the accessory oculomotor nuclei (nucleus interstitialis of Cajal, nucleus of Darkschewitsch, and nucleus of the posterior commissure), the mesencephalic reticular formation, the vestibular nuclei, the nucleus prepositus hypoglossi, and the cerebellar fastigial nucleus. The results are compared with previous anatomical investigations and confirm the electrophysiologically demonstrated FEF-PPRF-abducens disynaptic pathway.

Cortical Field Potentials Preceding Vocalization in Monkeys

Field potentials before vocalization were studied with electrodes chronically implanted on the surface and at a 2.0–3.0 mm depth in various cortical areas in three monkeys. Surface-negative, depth-positive (s-N, d-P) slow potentials prior to vocalization were recorded in the premotor (including the Broca's homolog), motor and somatosensory cortices, and the supplementary motor area (SMA). Such premovement potentials were recorded also in the cingulate and prefrontal cortices when a monkey uttered a sound with intense motivation for reward. Cerebellar hemispherectomy on the right side eliminated the s-N, d-P premovement potentials in the motor cortex and in the posterior bank of inferior limb of the arcuate sulcus (homolog of Broca's area) in the left hemisphere. After the operation, the tone came to have less components of different frequencies, and its duration varied much more than before. These facts suggest that the neocortical area homologous to the human speech area takes part in the generation and control of monkey vocalization together with the cerebellum possibly through cerebro-cerebellar interactions. This is against ideas so far proposed on nonhuman primate vocalization, i.e., it is generally considered that animal vocalization differs fundamentally from human speech.

Anatomic Organization of the Basilar Pontine Projections from Prefrontal Cortices in Rhesus Monkey

In our ongoing attempt to determine the anatomic substrates that could support a cerebellar contribution to cognitive processing, we investigated the prefrontal cortical projections to the basilar pons. A detailed understanding of these pathways is needed, because the prefrontal cortex is critical for a number of complex cognitive operations, and the corticopontine projection is the obligatory first step in the corticopontocerebellar circuit. Prefrontopontine connections were studied using the autoradiographic technique in rhesus monkey. The pontine projections were most prominent and occupied the greatest rostrocaudal extent of the pons when derived from the dorsolateral prefrontal convexity, including areas 8Ad, 9/46d, and 10. Lesser pontine projections were observed from the medial prefrontal convexity and area 45B in the inferior limb of the arcuate sulcus. In contrast, ventral prefrontal and orbitofrontal cortices did not demonstrate pontine projections. The prefrontopontine terminations were located preferentially in the paramedian nucleus and in the medial parts of the peripeduncular nucleus, but each cortical area appeared to have a unique complement of pontine nuclei with which it is connected. The existence of these corticopontine pathways from prefrontal areas concerned with multiple domains of higher-order processing is consistent with the hypothesis that the cerebellum is an essential node in the distributed corticosubcortical neural circuits subserving cognitive operations.

Corticocortical input to the smooth and saccadic eye movement subregions of the frontal eye field in Cebus monkeys.

1. The locations and connections of the smooth and saccadic eye movement subregions of the frontal eye field (FEFsem and FEFsac, respectively) were investigated in seven hemispheres of five Cebus monkeys. The supplementary eye field was also mapped in seven hemispheres and the hand/arm regions of the dorsal and ventral premotor areas were localized in five hemispheres. Monkeys were immobilized during experiments with Telazol, a dissociative anesthetic agent that has no significant effect on microstimulation-induced eye movement parameters (threshold, velocity, and duration). The functional subregions were defined with the use of low threshold intracortical microstimulation (current < or = 50 microA). Then different retrogradely transported fluorescent tracers were placed into these functionally defined regions. 2. The FEFsac in Cebus monkey is in the same location as the one in macaque monkeys, which is in Walker's areas 8a and 45. The FEFsem is located in the posterior shoulder of the superior arcuate sulcus near its medial tip and is therefore more accessible for tracer injections than the one in macaque monkeys. This subregion is within cytoarchitectural area 6a beta, which is distinct from the adjacent area 6a alpha (dorsal premotor area). This smooth eye movement subregion may be comparable with the one in macaque monkeys. 3. Cortical connection patterns of the FEFsac and FEFsem are similar and parallel to each other. The predominant neural input to these two subregions originates in other cortical eye fields, including the supplementary eye field, the parietal eye field, the middle superior temporal area, and the principal sulcus region. These cortical eye fields each contain two separate, almost non-overlapping, distributions of labeled neurons that project to the corresponding frontal eye field (FEF) subregions. These results suggest that there may be similar, but relatively independent, parallel corticocortical networks to control pursuit and saccadic eye movements. The weak connections between the middle temporal area (MT) and FEF suggest that the MT may not provide the major source of visuomotion inputs to the FEF, but that it rather plays a role in mediating visual information that is relayed from the striate and extrastriate cortices via MT to the parietal cortex and then to the FEF. In addition to the well-known neural connections between the lateral intraparietal area and the FEF, additional parietal projections have been demonstrated from the dorsomedial visual area area specifically to the FEFsac and from area 7m specifically to the FEFsem.

Functionally defined smooth and saccadic eye movement subregions in the frontal eye field of Cebus monkeys.

1. Intracortical microstimulation was used to localize and define the smooth and saccadic eye movement subregions of the frontal eye field (FEF) and the supplementary eye field (SEF) in nine hemispheres of six Cebus apella monkeys and to map the hand/arm areas in the dorsal premotor area and other adjacent areas in five hemispheres of three C. apella monkeys. Monkeys were anesthetized during experiments with Telazol, a dissociative agent that has no significant effect on microstimulation-induced eye movement parameters (current threshold, velocity, and duration). The functional subregions were defined with the use of low threshold current (< or = 50 microA). Electrically elicited eye movements were videotaped and quantified. The two types of eye movements were clearly distinguished by their significantly different duration and velocity (P < 0.0001) and their different responses to long stimulus trains. 2. The saccadic subregion of the FEF in Cebus monkeys is in the same location as in macaque monkeys (Walker's areas 8a and 45). Most of the functional and anatomic characteristics of the saccadic subregion of Cebus are the same as those reported in the saccadic FEF subregion of macaque monkeys. 3. A subregion in which only smooth eye movements were evoked was found in the posterior shoulder of the superior arcuate sulcus near its medial tip. A band of inexcitable cortex separated the SEF and this smooth eye movement subregion of the FEF. This supports the proposal that the smooth eye movement subregion is independent of the SEF but is analogous to the saccadic subregion of the FEF. The existence of two subregions of the FEF was further confirmed by single-unit recording results. It is proposed that the smooth eye movement subregion in Cebus monkeys may be comparable with the one described in macaque monkeys. 4. Both saccadic and smooth eye movements were also reliably evoked in the SEF in each hemisphere studied. This result strongly indicates that the SEF is concerned with not only saccadic eye movements, as previously reported, but also with smooth (pursuit) eye movements.

Field potential oscillatory bursts in parietal cortex before and during reach

Local field potentials were recorded in parietal cortex, areas 5, 7a and 7b, of a macaque monkey to determine if oscillatory bursts occurred in an observable relationship to behavioral events. The monkey performed a visually-guided reaching task to targets displayed on a touch-sensitive video monitor. The task was pre-cued with a 1.6 s preparatory period. Intracortical recordings were made with a microelectrode or epidural recordings with silver ball electrodes. Compared to the relaxed state, task performance was distinguished by a drop in power for frequencies below 20 Hz (most prominent in area 7), and an increase for frequencies above 20 Hz. For the β frequency band 20–25 Hz, maximal power occurred during the preparatory periods, and minimal power during reach performance. Above 30 Hz, reach preparation and performance episodes did not differ significantly in spectral power, except in parts of area 5 where 40 Hz activity was observed to increase during movement. The spatial extent of the β preparatory activity was monitored using an array of 15 epidural electrodes, positioned in 2 rows stretching from the arcuate sulcus to the lunate sulcus. During reach preparation, premotor cortex was found to be the major focus of increased power at 20 Hz, whereas posterior parietal cortex was the dominant focus of increased power in the 21–29 Hz band. Although β frequencies were most prevalent during early stages of motor preparation, the oscillatory bursts were not tightly time-locked to the visual signals. β Frequencies may be associated with an internally-triggered process to prepare the upcoming movement.

Neurons of the anterior mesial cortex related to faciovocal activity in the awake monkey.

1. The anterior mesial cortex, including the cingulate region, is thought to be involved in the voluntary control of vocalization. Previous recording studies have demonstrated that anterior mesial neurons discharge before conditioned and spontaneous vocalizations, but questions remain regarding the location and functional properties of these neurons. The present study was performed to provide a more complete description of the location and discharge properties of anterior mesial neurons involved in faciovocal behaviors. 2. Single-unit activity was recorded from neurons in the anterior mesial cortex of monkeys during performance of self-paced vocalizations and jaw openings. Cells were also tested for responsiveness to acoustic stimulation, and attempts were made to elicit vocalization through stimulation of the cortex surrounding related cells. Discharge properties of the cells were statistically analyzed, and correlation analysis was performed between measure of cell discharge and vocalization. 3. A total of 145 neurons were observed to modulate their discharge in association with vocalization or jaw opening. Four general classes of neurons were observed: neurons related only to vocalization, neurons related only to jaw opening, neurons related to both vocalization and jaw opening, and neurons related to other oromotor activities such as lip movements or reinforcement consumption. 4. Vocalization-related cells typically discharged tonically at a low frequency (mean 22 Hz), and many instances of long-lead activity (lead time > 500 ms) were noted. No neurons responded to acoustic stimulation, and electrical stimulation failed to elicit vocalization. Neural activity was not correlated with any measure of vocalization. 5. Neurons related to faciovocal behavior were located in the anterior cingulate sulcus and adjacent cortex of the mesial wall at a level just rostral to the genu of the arcuate sulcus. This region roughly corresponds to the rostral cingulate motor area and is located caudal to the traditionally described cingulate vocalization region. 6. In the present study we demonstrate the existence of an additional region in the medial wall that is involved in a variety of faciovocal behaviors such as vocalization, jaw opening, lip movements, and reinforcement consumption. The neurons do not appear to be strongly coupled to the execution of these acts. These results suggest that the activity of neurons in the anterior mesial cortex may relate to faciovocal behavior in a more global way than the activity of neurons in other motor areas.

Somatotopy of monkey premotor cortex examined with microstimulation

We reinvestigated the organization of the premotor cortex (PM) using intracortical microstimulation. Movements of forelimb, hindlimb, and orofacial structures were evoked from broad regions of PM that appeared to be contiguous with other motor areas. There were two principal findings: (1) the somatotopy of PM lies roughly parallel to that of the primary motor cortex (MI). Forelimb movements were evoked from sites deep in the caudal bank of the arcuate sulcus and throughout the adjacent cortex bounded by a face representation (laterally) and a hindlimb representation (medially and caudally); (2) unlike the MI, the PM forelimb representation overlaps significantly with its own face representation. PM hindlimb movement sites overlap only slightly with PM forelimb sites, in a manner similar to the MI. There was no obvious boundary between PM, Ml, or supplementary motor area hindlimb representations. The present findings are discussed in relation to recently identified subdivisions of the PM.

Cortical field potentials preceding vocalization and influences of cerebellar hemispherectomy upon them in monkeys

Field potentials preceding vocalization were recorded with electrodes chronically implanted on the surface and at 2.0–3.0 mm depth in various cortical areas in three monkeys. Surface-negative, depth-positive (s-N, d-P) slow potentials prior to vocalization were recorded in the premotor (including the Broca's homolog), motor and somatosensory cortices in both hemispheres, and the supplementary motor area in the cerebral hemisphere. Such premovement potentials were recorded also in the cingulate and prefrontal cortices when a monkey uttered with intense motivation for reward. Cerebellar hemispherectomy on the right side eliminated the s-N, d-P premovement potentials in the motor cortex and in the posterior bank of inferior limb of the arcuate sulcus (homolog of Broca's area) in the left hemisphere. Vocal tone contained less components in different frequencies, and its duration became more variable than before the operation. These facts suggest that the neocortical area homologous to the human speech area takes part in generation and control of monkey vocalization together with the cerebellum, possibly through cerebro-cerebellar interactions, against ideas so far offered on nonhuman primate vocalization.

Field potential change in the prefrontal cortex of the left hemisphere during learning processes of reaction time hand movement with complex tone in the monkey

Field potentials were recorded with electrodes implanted in various cortical areas while a naive monkey was learning reaction time hand movements with complex tone. When cortical surface-negative, depth-positive potential (at a latency of about 80 ms after a stimulus onset) appeared in the rostral bank of the inferior limb of the arcuate sulcus of the left cerebral hemisphere, and became gradually larger, the monkey began to respond to the stimulus with the movement. As the potential in the prefrontal (prearcuate) cortex and the cerebellar-mediated potential in the motor cortex gradually increased with further training, the movement became quicker and more skillful. Three naive monkeys achieved the movement with complex tone in shorter training days than the movement with pure tone; the movement with pure tone was not accompanied by any significant potential in the prefrontal cortex. It is deduced from the present study, and previous studies on visuo-initiated movements, that the prefrontal area, especially in the left hemisphere, plays a significant role for a monkey to associate a stimulus with appropriate motor execution.

A comparison of the ipsilateral cortical projections to the dorsal and ventral subdivisions of the macaque premotor cortex.

The cortical connections of the dorsal (PMd) and ventral (PMv) subdivisions of the premotor area (PM, lateral area 6) were studied in four monkeys (Macaca fascicularis) through the use of retrograde tracers. In two animals, tracer was injected ventral to the arcuate sulcus (PMv), in a region from which forelimb movements could be elicited by intracortical microstimulation (ICMS). Tracer injections dorsal to the arcuate sulcus (PMd) were made in two locations. In one animal, tracer was injected caudal to the genu of the arcuate sulcus (in caudal PMd [cPMd], where ICMS was effective in eliciting forelimb movements); in another animal, it was injected rostral to the genu of the arcuate sulcus (in rostral PMd [rPMd], where ICMS was ineffective in eliciting movements). Retrogradely labeled neurons were counted in the ipsilateral hemisphere and located in cytoarchitectonically identified areas of the frontal and parietal lobes. Although both PMv and PMd were found to receive inputs from other motor areas, the prefrontal cortex, and the parietal cortex, there were differences in the topography and the relative strength of projections from these areas. There were few common inputs to PMv and PMd; only the supplementary eye fields projected to all three areas studied. Interconnections within PMd or PMv appeared to link hindlimb and forelimb representations, and forelimb and face representations; however, connections between PMd and PMv were sparse. Areas cPMd and PMv were found to receive inputs from other motor areas--the primary motor area, the supplementary motor area, and the cingulate motor area--but the topography and strength of projections from these areas varied. Area rPMd was found to receive sparse inputs, if any, from these motor areas. The frontal eye field (area 8a) was found to project to PMv and rPMd, and area 46 was labeled substantially only from rPMd. Parietal projections to PMv were found to originate from a variety of somatosensory and visual areas, including the second somatosensory cortex and related areas in the parietal operculum of the lateral sulcus, as well as areas 5, 7a, and 7b, and the anterior intraparietal area. By contrast, projections to cPMd arose only from area 5. Visual areas 7m and the medial intraparietal area were labeled from rPMd. Relatively more parietal neurons were labeled after tracer injections in PMv than in PMd. Thus, PMv and PMd appear to be parts of separate, parallel networks for movement control.

Impairments on nonspatial self-ordered and externally ordered working memory tasks after lesions of the mid-dorsal part of the lateral frontal cortex in the monkey

Monkeys with lesions of the mid-dorsal part of the lateral frontal cortex, which extends above the sulcus principalis as far as the midline (MDL lesions), were shown to exhibit severe and long-lasting impairments on certain nonspatial working memory tasks: the self-ordered and externally ordered tasks (experiments 1, 2, 3, 5, 6, and 8). These tasks, which were modeled on similar ones previously used with patients, measure the capacity to monitor, within working memory, self-generated choices and the occurrence of externally ordered stimuli. Monkeys with lesions of the adjacent posterior dorsolateral frontal cortex, which surrounds the arcuate sulcus (PA lesions), performed as well as the normal control animals on these tasks. Experiments 4 and 5 showed that the critical variable accounting for the impairment on the self-ordered and externally ordered working memory tasks by monkeys with MDL lesions is the size of the set of stimuli that must be monitored. Furthermore, the MDL lesions did not affect basic recognition memory (experiment 6), or primacy and recency mnemonic effects [i.e., the capacity to discriminate between the initial (or final) items and other items in a list of stimuli (experiments 4 and 7), or the capacity to select from a set of stimuli on the basis of a learned fixed sequence (experiment 9)]. Thus, lesions of the mid-dorsal part of the lateral frontal cortex give rise to an impairment in working memory that depends on the size of the set of the stimuli that have to be monitored.

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.

Neural responses related to smooth-pursuit eye movements and their correspondence with electrically elicited smooth eye movements in the primate frontal eye field

1. Intracortical microstimulation of a portion of the monkey frontal eye field (FEF) lying in the floor and posterior bank of the arcuate sulcus evokes smooth, rather than saccadic eye movements. To further explore this region's involvement in pursuit, we recorded from FEF neurons in the vicinity of sites from which smooth eye movements (SEMs) were elicited electrically and studied their responses during smooth-pursuit and saccadic tasks. In this report, we describe the neurons' responses during visually guided smooth pursuit and compare their locations and response properties with those of elicited SEMs. 2. One hundred and ninety-three neurons, recorded from the FEF region in six hemispheres of three rhesus monkeys, were classified as "pursuit neurons". These neurons responded during smooth-pursuit tracking of moving visual stimuli but had no, or only minimal, responses in conjunction with visually guided saccades. Pursuit neurons were located in a small region of the arcuate fundus and posterior bank that overlapped, and extended slightly beyond, the region from which SEMs were elicited with microstimulation. 3. All pursuit neurons had a preferred pursuit direction, and all directions were represented with no strong bias toward ipsilateral, contralateral, up, or down. The directional tuning of 80 pursuit cells was measured quantitatively by testing pursuit in several directions and fitting the responses to a Gaussian function. Tuning indices (the sigma parameter of the Gaussian fit) varied between 13 degrees and 136 degrees. The median tuning index, 44.5 degrees, corresponds to a full width at half maximum of 105 degrees. The ubiquity of selectivity for pursuit direction and the wide distribution of preferred directions indicates that pursuit direction uses a place-code type of representation in FEF; however, the broad directional tuning of most neurons suggests that pursuit direction is given by a weighted average of optimal directions across the population of pursuit neurons active at any given time. 4. In general, the responses of pursuit neurons increased with pursuit velocity. Of 13 neurons formally tested with 2 s of constant-velocity tracking in their preferred direction across a range of target speeds, pursuit velocity sensitivity ranged from 0.24 to 1.42 spikes.s-1.deg-1.s-1, with an average sensitivity of 0.70. This relationship suggests that pursuit neurons represent pursuit magnitude using a rate code; this parallels our previous observation that at most SEM sites, the velocity and acceleration of the electrically elicited eye movements increased as a function of the stimulation current.(ABSTRACT TRUNCATED AT 400 WORDS)

Force-related neuronal activity in two regions of the primate ventral premotor cortex

Neuronal activity was recorded in the ventral premotor cortex of one monkey (Macaca fascicularis) trained to exert finely graded forces with thumb and index finger on a force sensor in a visuomotor step-tracking paradigm. Trials with two or three consecutive ramp-and-hold force steps were presented randomly. Most neurons displayed similar discharge patterns in the two- and three-step trials and were assigned to one of the following classes: phasic, phasic-tonic, tonic, decreasing, and mixed. For more than 50% of the neurons with tonic activity, positive or negative correlations between firing rate and force were statistically significant. The indices of force sensitivity were on average higher for the two-step than for the three-step trials, indicating that the correlations yielded linearity over only a limited force range. The force-related cells were located in two regions of the ventral premotor cortex. One group was ying rostrally within the inferior limb of the arcuate sulcus, from which microstimulation elicited movements of fingers and hand. In the other more caudal region, adjacent to the finger region of primary motor cortex, microstimulation was rarely effective, but all neurons had clear peripheral receptive fields on finger and hand. The data indicate that two populations of neurons, located in the ventral premotor cortex, are related to movement execution. Effective microstimulation also suggests that one of the populations has fairly direct access to the spinal motor apparatus.

Direct projections from the ventral premotor cortex to the hindlimb region of the supplementary motor area in the macaque monkey

A retrograde tracer, Diamidino yellow, was injected into the hindlimb region of the supplementary motor area after intracortical microstimulation mapping in the Japanese monkey. As a result, a cluster of retrogradely labeled neurons was found in the caudal bank of the arcuate sulcus, which corresponds to the ventral premotor cortex. The present findings suggest that there exists a hindlimb representation in the ventral premotor cortex.

Differential effects of muscimol microinjection into dorsal and ventral aspects of the premotor cortex of monkeys.

1. A gamma aminobutyric acid (GABAA) receptor agonist, muscimol (Sigma, 5 micrograms/microliters solution), and a GABAB receptor agonist and antagonist, baclofen and phaclofen, respectively, were injected (1.0 microliter) into the dorsal and ventral aspects of the premotor cortex (PM) of two Japanese monkeys (Macaca fuscata), while they were performing a motor task that required wrist flexion or extension to a target. The correct movement was instructed by either 1) a conditional color cue [green or red light emitting diodes (LED)] equidistant from the targets or 2) a directional cue toward extension or flexion (right or left LED). When the green or right LED was illuminated, extension was to be performed. When the red or left LED was illuminated, flexion was required. The movement was triggered by a visual stimulus either simultaneously with the instruction stimulus or after a variable delay. 2. Before drug injection, single-unit recordings were made to select injection sites 1) in the dorsal aspect of the PM (PMd) around the superior precentral sulcus where typical set-related activity was frequently recorded and 2) in the ventral aspect of the PM (PMv) immediately caudal to the genu of the arcuate sulcus where movement-related neurons were densely located. 3. Behavioral deficits were observed primarily at the time muscimol, but not baclofen or phaclofen, was injected. Furthermore, muscimol effects were short-lasting: deficits were most frequently observed during the 10-min injection period but seldom after completion of injection. 4. When muscimol was injected into the PMd, there was an increase in the number of direction errors primarily when the conditional cues were presented. The initiated movements were similar in amplitude and velocity to the preinjection behavior. In contrast, when muscimol was injected into the PMv, many of the initiated movements showed smaller amplitudes and slower velocities, but few direction errors were made. 5. These results suggest that the PMd and PMv play differential roles in motor control: the PMd is more important than PMv in conditional motor behavior and plays a role in the preparation for forthcoming movements. In contrast, the PMv is more specialized for a role in the execution of visually guided movements.

Connections of inferior temporal areas TEO and TE with parietal and frontal cortex in macaque monkeys.

Inferior temporal cortex is perhaps the highest visual processing area and much anatomical work has focused on its connections with other visual areas in temporal and occipital cortex. Here we report connections of inferior temporal cortex with regions in the frontal and parietal lobes. Inferior temporal areas TEO and TE were injected with WGA-HRP and 3H-AA, respectively, or vice versa, in 1-week-old infant and 3-4-year-old adult monkeys (Macaca mulatta). The results indicated that whereas TEO has more extensive connections with parietal areas, TE has more extensive connections with prefrontal areas. Thus, in the intraparietal sulcus, area TEO is connected with areas LIPd, LIPv, and V3A, and with the as yet undefined region between LIPv and V3A, whereas the connections of TE are predominantly with LIPd, and to a lesser extent with LIPv. In the prefrontal cortex, area TE is connected with areas 8 and 45 in the inferior limb of the anterior bank of the arcuate sulcus, with area 12 on the inferior prefrontal convexity, and with areas 11 and 13 on the orbital surface. By contrast, the connections of area TEO are limited to areas 8, 45, and 12. Furthermore, within prefrontal cortex, the projections from areas TEO and TE terminate in different layers in areas 8 and 45, such that those from TEO terminate in all layers, whereas those from TEO terminate in layers I and V/VI only. In contrast to the connections of areas TEO and TE with various medial temporal-lobe and subcortical structures, which are immature in infant monkeys (Webster et al., 1991, 1993b), the connections with parietal and prefrontal areas appear adult-like as early as 1 week of age.