Spatial cortical patterns of metabolic activity in monkeys performing a visually guided reaching task with one forelimb.

The 2-[14C]deoxyglucose method was used to map the metabolic activity in the neocortex of monkeys (Macaca nemestrina) performing a visually guided reaching task with one forelimb. Monkeys received liquid reward for correct, single directional reaching movements, which were required at a rate of about 10 per minute. We estimated the weighted average of local glucose consumption within several neocortical areas, and we reconstructed quantitative, high-resolution, two-dimensional maps of the detailed spatiointensive patterns of activity. Our findings demonstrate the involvement of the striate and prestriate cortices, the inferior intraparietal and superior temporal visual association areas, the frontal eye field and the caudal periprincipal cortex, the primary somatosensory and the related superior intraparietal area, the primary and association auditory cortices, the superior temporal multimodal region, and the premotor, primary, supplementary, and cingulate motor areas. The visual cortex in the superior temporal and the intraparietal sulci, which is concerned with "where", was activated during visually guided reaching. In contrast, the inferior temporal visual association cortex, which is concerned with "what", was not involved in our study. We suggest that the activated direction-selective layer four of V1 and the thick stripes of V2 convey visuomotor information to the activated cortex in the posterior bank and the floor of the superior temporal sulcus, which may encode the constantly updated position of the moving forelimb. In parallel, the activated cortex in the ventral part and the lateral bank of the intraparietal sulcus may encode visuospatial information related to the localization of the visual target in the extrapersonal space. Furthermore, the dorsal part of the medial bank of the intraparietal sulcus may be involved in proprioceptive guidance of movement, based on the parallel metabolic effects shown only contralateral to the moving forelimb within this region and the forelimb representations in the primary somatosensory and motor cortices. Finally, the bilaterally activated network including the inferior postarcuate skeletomotor and prearcuate oculomotor cortical fields and the caudal periprincipal region 46 may participate in sensory and oculomotor to motor transformations, in parallel with the medial and lateral intraparietal cortices with which this network is reciprocally interconnected.

Metabolic activity pattern in the motor and somatosensory cortex of monkeys performing a visually guided reaching task with one forelimb.

The [14C]deoxyglucose method was used to map the metabolic activity in the primary somatosensory and motor cortex in monkeys (Macaca nemestrina) performing a unimanual task. The task required visually guided reaching and target holding at a rate of about 10 movements per min. The entire dorsoventral extent of the cortical region lying between the posterior crown of the arcuate and the anterior crown of the intraparietal sulci was reconstructed on the sagittal plane, from horizontal sections aligned on the fundus of the central sulcus. The metabolic mapping of the control monkey demonstrated homogeneous activity all around the central sulcus, bilaterally. The mapped activity in the performing monkeys displayed two different patterns. The first pattern, contralateral to the moving forelimb, was characterized by several discrete regions of increased metabolic activity, which were symmetrically distributed in a mirror image fashion around the fundus of the central sulcus. These activated regions correspond to the lower body, forelimb, and mouth areas of representation of body parts in previously reported maps in primary motor and somatosensory cortical areas. The second activity pattern ipsilateral to the moving forelimb, displayed activated somatosensory and motor regions corresponding only to the lower body, and mouth representations. Our study provides a continuous, high resolution map of activity pattern in the entire primary motor and somatosensory cortices, which demonstrates that the reaching forelimb is controlled by a discrete subregion in the contralateral somatosensorimotor cortex, whereas other subregions of body representation are actively involved, bilaterally, during the performance of a relatively simple motor behaviour.

Functional anatomy of the thalamic reticular nucleus as revealed with the [14C]deoxyglucose method following electrical stimulation and electrolytic lesion.

The [14C]-deoxyglucose quantitative autoradiographic method was used to map the metabolic changes induced by electrical stimulation and electrolytic lesion of the rostral pole of the thalamic reticular nucleus in the rat brain. Unilateral electrical stimulation of the thalamic reticular nucleus induced the following changes in glucose utilization: (i) local enhancement of metabolic activity within the stimulated thalamic reticular nucleus, (ii) increase in glucose consumption in the ipsilateral thalamic mediodorsal, centrolateral, ventromedial and ventrolateral nuclei, as well as in the nucleus accumbens, (iii) bilateral depression of metabolism in the locus coeruleus, periaqueductal gray, ventral tegmental area, and medial habenula, as well as contralateral metabolic depression in the substantia nigra reticulata, compacta and in the ventral pallidum. Unilateral electrolytic lesion of thalamic reticular nucleus elicited metabolic depression in the ipsilateral thalamic mediodorsal, centrolateral, ventrolateral and ventromedial nuclei, and metabolic activation in the dorsal tegmental nucleus bilaterally. The existence of a descending thalamic reticular nucleus input to the periaqueductal gray is supported by the depressed activity measured in brain stem structures after thalamic reticular nucleus stimulation. The similar effects observed in the periaqueductal gray and substantia nigra contralateral to the stimulated thalamic reticular nucleus indicate a possible flow of information from one thalamic reticular nucleus to the contralateral basal ganglia via the periaqueductal gray. The opposite effects induced in the dorsal thalamic nuclei by thalamic reticular nucleus stimulation and lesion support the gating role of the thalamic reticular nucleus in the information flow between thalamus and cortex.

Functional anatomy of the thalamic centrolateral nucleus as revealed with the [14C]deoxyglucose method following electrical stimulation and electrolytic lesion.

The effects of electrical stimulation and electrolytic lesion of the thalamic intralaminar centrolateral nucleus were studied in the rat brain by means of the quantitative autoradiographic [14C]deoxyglucose method. Unilateral electrical stimulation of the centrolateral nucleus induced: (i) local increase in metabolic activity within the stimulated centrolateral nucleus and the ipsilateral thalamic mediodorsal nucleus, (ii) metabolic depression in all layers of the ipsilateral frontal cortex, (iii) bilateral increase in glucose consumption within the periaqueductal gray, pedunculopontine nucleus, and pontine reticular formation, and (iv) contralateral metabolic activation in the deep cerebellar nuclei. The unilateral electrolytic lesion of the thalamic centrolateral nucleus elicited metabolic depressions in several distal brain areas. The metabolic depression elicited in the mediodorsal, ventrolateral, and lateral thalamic nuclei, as well as in the caudate nucleus, the cingulate, and the superficial layers of forelimb cortex were ipsilateral to the lesioned side. The metabolic depression measured in the medulla and pons (medullary and pontine reticular formation, periaqueductal gray, locus coeruleus, dorsal tegmental, cuneiformis, raphe and pedunculopontine tegmental nuclei), the cerebellum (molecular and granular layers of the cerebellar cortex, interpositus and dentate nuclei), the mesencephalon (substantia nigra reticulata, ventral tegmental area and deep layers of the superior colliculus), the diencephalon (medial habenula, parafascicular, ventrobasal complex, centromedial and reticular thalamic nuclei), the rhinencephalon (dentate gyrus and septum), the basal ganglia (ventral pallidum, globus pallidus, entopeduncular and accumbens nuclei) and the cerebral cortex (superficial and deep layers of the frontal and parietal cortex, deep layers of the forelimb cortex) were bilateral. These functional effects are discussed in relation to known anatomical pathways. The bilateral effects induced by the centrolateral nucleus lesion reflect an important role of the centrolateral nucleus in the processing of reticular activating input and in the interhemispheric transfer of information. The cortical metabolic depression induced by centrolateral nucleus stimulation indicates the participation of this nucleus in attentional functions.

Bilateral cerebral metabolic effects of pharmacological manipulation of the substantia nigra in the rat: unilateral intranigral application of the inhibitory GABAA receptor agonist muscimol.

Rates of cerebral glucose utilization were measured by means of the autoradiographic 2-deoxy-D[1-14C]glucose technique in the rat brain in order to determine the metabolic effects of unilateral intranigral application of the GABAA agonist muscimol upon the substantia nigra and its targets. Intranigral injection of 1.5 microliters 0.3 M muscimol (52 micrograms total dose) induced local metabolic activation in the injected substantia nigra reticulata (by 87% as compared to the control group), and distal metabolic depressions in the nucleus accumbens, striatum, globus pallidus and subthalamic nucleus only ipsilaterally to the injected nigra. The remaining basal ganglia components, including the substantia nigra compacta and the entopeduncular nucleus were bilaterally unaffected. Among the principal efferent projections of the substantia nigra reticulata, the ventromedial and centrolateral thalamic nuclei as well as the deep layers of the superior colliculi were metabolically depressed bilaterally, whereas the ventrolateral, parafascicular and mediodorsal thalamic nuclei as well as the pedunculopontine nucleus displayed metabolic depressions ipsilateral to the muscimol-injection nigra. The ventromedial and centrolateral thalamic nuclei were depressed by 41 and 42%, respectively, in the ipsilateral side, and by 30 and 26% in the contralateral side, when compared to the respective values of the control group of rats. Furthermore, unilateral intranigral injection of 0.3 M muscimol induced metabolic depressions in reticular, intralaminar and prefrontal thalamocortical areas mostly ipsilateral to the injected nigra, as well as in limbic areas bilaterally. It is suggested that the present findings are due to a postsynaptic effect of muscimol on the nigral GABAergic cells and to a consequent metabolic depression of the basal ganglia and associated thalamocortical areas, in contrast to an earlier suggested presynaptic nigral effect of lower doses of intranigrally injected muscimol which induced metabolic activations within the same network. This suggestion is further supported by the fact that intranigrally injected substrate P19 induced similar effects to those elicited by the lower doses of intranigral muscimol and opposite to those induced at present by the higher muscimol dose. Moreover, it is further substantiated that the nigrothalamic GABAergic system is responsible for considerable transfer of information from one substantia nigra reticulata to the ipsilateral basal ganglia and associated thalamocortical components as well as to bilateral motor, intralaminar and limbic areas.