Ipsilateral cortico-cortical and thalamo-cortical projections to the cat motor cortex were determined from the locations of retrogradely labeled neurons following single small intracortical injections of HRP in area 4 gamma. These projections were also examined by studying the distribution of anterogradely transported axonal label following multiple injections of HRP or of tritiated amino acids in areas 1-2 of SI and in area 2pri (SII). The number of retrogradely labeled cells in areas 1-2 and in area 2pri differed markedly between HRP injection sites located in the precruciate (anterior sigmoid gyrus) and postcruciate (posterior sigmoid gyrus) subregions of area 4 gamma. These associational projections from primary and secondary somatosensory cortices were dense to postcruciate subregions but weak to the precruciate subregions. The associational projections from areas 1-2 and from area 2pri to the postcruciate subregion of area 4 gamma were topographically organized, but no clear topographic organization could be demonstrated for the precruciate projection. Anterograde terminal labeling following injection of either HRP or tritiated amino acids into areas 1-2 and area 2pri confirmed the preferential projection of somatosensory cortex to the postcruciate subregion of motor cortex. The projection from somatosensory areas 1-2 was uniform over its terminal field, but that from area 2pri was more patchy and complex. HRP injections in area 4 gamma gave rise to lamellae of labeled neurons in the ventrolateral nucleus of thalamus (VL). A topographic relationship was found between the site of injection and the location of the lamella of labeled neurons. The percentage of retrogradely labeled neurons in the shell zone surrounding the border of the ventrolateral nucleus and the ventrobasal complex (VB) was greater following postcruciate than precruciate injections, whereas fewer retrogradely labeled neurons were found in central lateral nucleus (CL) after postcruciate injections than after precruciate injections. These observations support the hypothesis that differential cortical and thalamic projections to different subregions of area 4 gamma may give rise to the different physiological properties of neurons observed in these subregions (Vicario et al. 1983; Martin et al. 1981).
We have shown (Asanuma et al., 1979c) that the monkey motor cortex receives peripheral somesthetic inputs directly from the thalamus. In the present experiments, we studied the pathways which mediated these inputs by stimulating superficial radial (SR) and deep radial (DR) nerves and recording evoked potentials from the motor and sensory cortices and the following results were obtained: 1. The focus for SR and DR evoked potentials in the sensory cortex was located in a circumscribed small area whereas in the motor cortex, the evoked potentials were distributed in a wide area along the central sulcus including the distal forelimb area. 2. Ablation of the sensory cortex reduced the size, but neither abolished nor changed the latency of the evoked potentials in the motor cortex. 3. Section of dorsal column nearly abolished the evoked potentials in the motor cortex, but only halved their size in the sensory cortex. 4. Section of ventrolateral cervical column including the spinothalamic tract halved the size of evoked potentials in the sensory cortex, but did not change the size in the motor cortex. 5. It is concluded that direct peripheral inputs to the motor cortex are mediated primarily through the dorsal column system whereas the peripheral inputs to the sensory cortex are mediated through both dorsal column and spinothalamic tract.
Many neurons in the inferior dorsolateral area of the monkey prefrontal cortex showed sustained increases in discharge rates during continuous gazing at a tiny light spot that had a reward significance. These increases might depend upon stimulus factors (light target), behavioral factors (gazing) or both. In this report, we tried to separate these factors and to test the extent to which each factor might contribute to the neuronal reaction. Monkeys were trained to exhibit two kinds of behavior : 1) maintained gazing at a light target and 2) "gazing" behavior without a clear target. We then examined neuronal behavior in these two kinds of gazing behavior. During "gazing at target," many prefrontal neurons showed tonic activation ; thus the previous findings were confirmed. These neurons behaved in various ways in "gazing without target" : 1) some of the neurons were activated to the same extent as in "gazing at target" ; 2) many others also showed activation but with lower discharge rates; and 3) the rest of the neurons completely ceased activation. Such variation in discharge patterns may be interpreted as meaning that there is a continuous and graded difference among individual neurons in the dependence of their gaze-related activation upon a visible target. Then it seems that the stimulus factors are involved in a graded manner in generation of the activation, and further that other factors, probably behavioral ones, also contribute in part to it.Recent investigations have revealed that during delayed-response tasks many neurons in the prefrontal cortex exhibit increased discharge rates with various patterns. Activation is seen during the presentation of the pre-delay cue, the delay period and/or animals' responses upon cue presentation (FUSTER, 1973;KUBOTA et al., 1974). Such activation of prefrontal cortical neurons may be related to the choice and use of visual cues in delayed-response performance. However, the variety of activation patterns seen and the rather complex sequence of stimulus and behavioral events present in this task have impeded further analysis
The topographic organization of somatosensory input to the primate red nucleus was investigated by studying receptive fields of rubral neurons, and that of the motor output by delivering trains of microstimulating pulses to evoke movements. A receptive field was identified in 191 of 208 rubral neurons. Most neurons (172) responded to passive movement of one or two joints including digits but some (26) had a cutaneous input. Neurons in both the parvocellular (RNpc) and magnocellular (RNmc) divisions of the nucleus had receptive fields. Neurons which responded to stimulation of the forelimb were located in the dorsomedial part of the nucleus. Those responsive to stimulation of the hindlimb were in the ventrolateral part. Thin regions on the dorsal and ventrolateral borders of the nuclei, respectively, contained neurons responsive to face and tail stimulation. Within the regions representing each limb, neurons receiving an input from the extremity (hand or foot) formed a core surrounded by neurons with an input from more proximal segments. This core extended uninterrupted throughout the RNpc and RNmc. Movements of individual limb segments including digits were readily evoked by microstimulating in the RNmc with thresholds as low as 3 microA. In most cases, movements were evoked in the direction opposite to the passive movement which drove the neurons at the stimulating site, although fibers of passage limited the analysis of the sensory input-motor output organization with stimulation. We conclude that there is topographic localization of somatosensory input and motor output in the macaque red nucleus. Furthermore, the red nucleus of monkeys contributes to the control of independent movements of limb segments including digits, although the number of axons it sends to the spinal cord is less than 1% of the number of corticospinal axons.
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