Ikuma Hamada

Organization of inputs from cingulate motor areas to basal ganglia in macaque monkey

The cingulate motor areas reside within regions lining the cingulate sulcus and are divided into rostral and caudal parts. Recent studies suggest that the rostral and caudal cingulate motor areas participate in distinct aspects of motor function: the former plays a role in higher‐order cognitive control of movements, whereas the latter is more directly involved in their execution. Here, we investigated the organization of cingulate motor areas inputs to the basal ganglia in the macaque monkey. Identified forelimb representations of the rostral and caudal cingulate motor areas were injected with different anterograde tracers and the distribution patterns of labelled terminals were analysed in the striatum and the subthalamic nucleus. Corticostriatal inputs from the rostral and caudal cingulate motor areas were located within the rostral striatum, with the highest density in the striatal cell bridges and the ventrolateral portions of the putamen, respectively. There was no substantial overlap between these input zones. Similarly, a certain segregation of input zones from the rostral and caudal cingulate motor areas occurred along the mediolateral axis of the subthalamic nucleus. It has also been revealed that corticostriatal and corticosubthalamic input zones from the rostral cingulate motor area considerably overlapped those from the presupplementary motor area, while the input zones from the caudal cingulate motor area displayed a large overlap with those from the primary motor cortex. The present results indicate that a parallel design underlies motor information processing in the cortico‐basal ganglia loop derived from the rostral and caudal cingulate motor areas.

Thalamocortical and intracortical connections of monkey cingulate motor areas

Although there has been an increasing interest in motor functions of the cingulate motor areas, data concerning their input organization are still limited. To address this issue, the patterns of thalamic and cortical inputs to the rostral (CMAr), dorsal (CMAd), and ventral (CMAv) cingulate motor areas were investigated in the macaque monkey. Tracer injections were made into identified forelimb representations of these areas, and the distributions of retrogradely labeled neurons were analyzed in the thalamus and the frontal cortex. The cells of origin of thalamocortical projections to the CMAr were located mainly in the parvicellular division of the ventroanterior nucleus and the oral division of the ventrolateral nucleus (VLo). On the other hand, the thalamocortical neurons to the CMAd/CMAv were distributed predominantly in the VLo and the oral division of the ventroposterolateral nucleus‐the caudal division of the ventrolateral nucleus. Additionally, many neurons in the intralaminar nuclear group were seen to project to the cingulate motor areas. Except for their well‐developed interconnections, the corticocortical projections to the CMAr and CMAd/CMAv were also distinctively preferential. Major inputs to the CMAr arose from the presupplementary motor area and the dorsal premotor cortex, whereas inputs to the CMAd/CMAv originated not only from these areas but also from the supplementary motor area and the primary motor cortex. The present results indicate that the CMAr and the caudal cingulate motor area (involving both the CMAd and the CMAv) are characterized by distinct patterns of thalamocortical and intracortical connections, reflecting their functional differences. J. Comp. Neurol. 462:121–138, 2003.

Characteristics of the ipsilateral movement-related neuron in the motor cortex of the monkey

The characteristics of the precentral neuron activity related to ipsilateral movements were studied while the monkey was performing finger, wrist and arm movements on either side. Out of 197 task-related neurons, 134 discharged in association with contralateral movements, but not with any one of 3 ipsilateral movements. Fifty neurons discharged with bilateral movements. Thirteen neurons discharged in association with ipsilateral movements (ipsi-neurons). Ten were recorded from the trunk or shoulder area of the motor cortex and were accompanied by contraction of those muscles by intracortical stimulation (ICS). The remaining 3 were related to elbow or wrist, but no ipsi-neurons were related to finger muscle contractions. In ipsilateral task performance, 7 ipsi-neurons discharged in association with finger and/or wrist movements in addition to arm movement. Five others were associated with arm movement. The last one discharged with wrist movement. Most of the units showed similar response to contralateral movement. Ipsi-neurons were classified into two groups. One group was recorded around the sulcus precentralis superior, had the lower threshold current and was mostly associated with finger, wrist and arm movements. The other was recorded in the rostral motor cortex, and had the higher threshold current and was related to arm movement. Among 185 neurons to which pyramidal tract stimulation was delivered, 2 out of the 80 PTNs and 11 out of the 105 non-PTNs were ipsi-neurons. EMGs were recorded from various muscles involved in the forelimb movements. Arm and finger muscles showed no activity when the monkey used the ipsilateral hand, while most of the shoulder and trunk muscles showed tonic or moderate transient changes in the activity during the ipsilateral tasks. The ipsi-neuron activity was discussed in consideration with EMGs.

Morphological differences between fast and slow pyramidal tract neurons in the monkey motor cortex as revealed by intracellular injection of horseradish peroxidase by pressure

Abstract Morphological differences between 4 fast and 3 slow pyramidal tract neurons (PTNs) in the monkey motor cortex were studied by intracellular injection of horseradish peroxidase (HRP). Fast PTNs had larger soma and thicker axons than slow PTNS and had two to three tap root basal dendrites. An apical dendrite of fast PTNs had a narrow dendritic field with fewer branches, and was free of spines in layers I and II. Axon collaterals of both PTNs did not reach layer III. The narrow apical dendritic field of fast PTN may be important to the reception of restricted inputs and to perform skillful movement.

Topographical projections from the prefrontal cortex to the post-arcuate area in the rhesus monkey, studied by retrograde axonal transport of horseradish peroxidase

The cells of origin of ipsilateral, prefrontal cortical projections to the post-arcuate area were studied in rhesus monkeys with the horseradish peroxidase (HRP) method. Following injections of HRP into the dorsal portion of the post-arcuate area, retrogradely labeled cells appeared in the arcuate area dorsal to the principal sulcus, while, following injections into its ventral portion, labeled cells appeared in the arcuate area ventral to the principal sulcus. They were pyramidal cells and lay mainly in the III layer, but small numbers of them were also found in the IV and V layers. In addition, HRP labeled cells were seen ipsilaterally in the banks of the cingulate sulcus.

A modified microsyringe for extracellular recording of neuronal activity

We describe a modified Hamilton microsyringe that allows extracellular recording of neuronal activity and subsequent injections. It is assembled with a Hamilton removable needle and a syringe for injection, a Teflon-coated tungsten wire for recording, and polyimide tubing as a sheath. The device is inexpensive and easy to handle in anatomical and physiological experiments in awake monkeys.

Monkey pyramidal tract neurons and changes of movement parameters in visual tracking.

During a single-step visual tracking task of monkeys, parametric changes of the wrist extension-flexion movement and related discharge rate changes of pyramidal tract neurons (PTNs) of hand-arm motor area were studied. The task consisted of preparatory, precontraction, contraction and target periods. If the displacement amplitude was changed from narrow (10-20 degrees) to moderate (40 degrees) range, peak velocity, peak acceleration and contraction period increased linearly but precontraction period decreased slightly. In 61 movement-related PTNs, no linear relationships were found between PTN discharge rate during precontraction or contraction period and displacement amplitude, velocity, acceleration, precontraction period or contraction period. In less than 20% of PTNs, however, correlations between PTN discharge rate during precontraction period and velocity or acceleration were found in the moderate range task. It occurred less frequently in narrow range task. It is said in a visual tracking task that PTN activity is not dependent upon factors related to the task parameters, such as velocity, acceleration. Possible related factors were discussed.

A cortical motor region that represents the cutaneous back muscles in the macaque monkey

A cortical motor region that represented the cutaneous muscles on the back was identified on the medial wall of the frontal lobe in the macaque monkey. In this region, neurons responded to somatosensory stimuli such as light touch or squeezing of the back skin, and intracortical microstimulation elicited contraction of the back skin. Such a region was located primarily on the dorsal bank of the cingulate sulcus, corresponding to the dorsal cingulate motor area.

Correlation of monkey pyramidal tract neuron activity to movement velocity in rapid wrist flexion movement.

The activity of 41 pyramidal tract neurons (PTNs) within the hand-arm area of the monkey motor cortex was studied during a rapid wrist flexion movement at specified velocities. The discharge rate during the movement showed significant correlations to the movement velocity in 21 PTNs, but the rate before the movement onset did not show correlations. Therefore the PTN activity before the movement onset in the rapid wrist flexion is not coding the velocity of the movement.

Microelectrode findings and topographic reorganisation of kinaesthetic cells after gamma knife thalamotomy.

SummaryA 64-year-old woman with Parkinson is disease had a severe resting tremor that was not completely relieved by right-sided gamma knife thalamotomy (GKT). We performed bilateral staged thalamic deep brain stimulation (DBS) and compared the right and left ventral intermediate nucleus (Vim) of the thalamus including the frequency of single units recorded with microelectrodes, and also the somatotopical distribution of kinaesthetic cells (Ki). The average frequency of units for the presumed left Vim exceeded that of the right (22.6 ± 19.2 Hz vs. 14.3 ± 8.8 Hz). Regarding the somatotopic distribution of Ki, the receptive field for the leg, which is usually situated in the dorsolateral Vim, was more widely scattered in the right Vim than the non-lesioned left side. Our findings raise the possibility that the specific properties of the neurons changed due to partial coagulation by GKT within both the coagulated and the surrounding thalamic lesions.