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PubMed2000

Specific versus nonspecific brain activity in a parametric N-back task.

In this study functional magnetic resonance imaging (fMRI) was used to examine cerebral activity patterns in relation to increasing mental load of a working memory task. Aim of the experiment was to distinguish nonspecific task-related processes from specific workload processes analytically. Twelve healthy volunteers engaged in a spatial n-back task with four levels. FMRI data were acquired with the 3D-PRESTO pulse sequence. Analysis entailed a two-step multiple regression algorithm, which was specifically designed to measure and separate load-sensitive and load-insensitive activity simultaneously, while preserving the original high spatial resolution of the fMRI signal. Load-sensitive and load-insensitive activity was found in both dorsolateral-prefrontal and parietal cortex, predominantly bilaterally, and in the anterior cingulate. As expected, the left primary sensorimotor cortex showed predominantly load-insensitive activity. Load-sensitive activity reflects specific working memory functions, such as temporary retention and manipulation of information, while load-insensitive activity reflects supportive functions, such as visual orientation, perception, encoding, and response selection and execution. Good performance was correlated with a large area of load-sensitive activity in anterior cingulate, and with a small area of load-insensitive activity in the right parietal cortex. The findings indicate that nonspecific and specific working memory processes colocalize and are represented in multiple frontal and parietal regions. Implication of this analytical strategy for application in research on psychiatric disorders is discussed.

Adult↗

PubMed1999

Imaging functional activation of the auditory cortex during focal repetitive transcranial magnetic stimulation of the primary motor cortex in normal subjects.

Positron emission tomography (PET) during focal repetitive transcranial magnetic stimulation (rTMS) has emerged as a promising approach to study cortical connectivity in awake humans. However, the noise caused by the discharging magnetic coil might have confounding effects on the rTMS-related cortical activation pattern. In twelve healthy volunteers, 18-fluoro-2-deoxy-D-glucose (18FDG) PET was employed to visualize the functional activation of the primary auditory cortex (PAC) during 2 Hz rTMS of the left primary sensorimotor hand area. Magnetic stimuli (1800) were applied at an intensity of 140% of motor resting threshold during the uptake period of 18FDG. Though all subjects wore earplugs, rTMS-related noise induced a consistent bilateral increase of regional glucose utilization in the PAC (P < 0.05, corrected). Thus, rTMS-related acoustic input needs to be taken into account in combined rTMS/PET studies.

Adult↗

PubMed1998

Associative and limbic regions of monkey striatum express high levels of dopamine D3 receptors: effects of MPTP and dopamine agonist replacement therapies.

The role of the dopamine D3 receptor subtype in the central nervous system is still not well understood. It has a distinct and restricted distribution, mostly associated with limbic territories of the striatum (olfactory tubercle and the shell of nucleus accumbens) in rat brain. Dopaminergic denervation induced by a 6-hydroxydopamine lesion of the nigrostriatal system in rat down-regulates the expression of the D3 receptor. In the present study, we investigated the functional neuroanatomy of the dopamine D3 receptor subtype in the monkey (Macaca fascicularis) basal ganglia. We also studied the effect of administration of the dopaminergic neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and chronic D1-like (SKF 82958) or D2-like (cabergoline) agonist treatments on dopamine D3 receptor levels using receptor autoradiography. Our results clearly show that the distribution of D3 receptors in the monkey is more closely related to associative and limbic components of the striatum (caudate-putamen), as compared with its sensorimotor counterpart. Hence, D3 receptors may be more specifically involved in cognitive and motivational aspects of striatal functions, which are elaborated in prefrontal, temporal, parietal, cingulate and limbic cortices. Moreover, MPTP administration significantly decreased levels of D3 receptors and this effect was reversed or compensated by a chronic treatment with a D1-like, but not a D2-like, receptor agonist. The D3 receptor may represent an important target for adjunct or direct therapy designed to improve cognitive deficits observed in patients with Parkinson's disease, schizophrenia and other illnesses with frontal lobe cognitive disturbances.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗

PubMed1990

Rescuing neurons from trans-synaptic degeneration after brain damage: helpful, harmful, or neutral in recovery of function?

Certain instances of neuronal degeneration secondary to brain damage might be functionally beneficial, and steps taken to protect against such degeneration may adversely affect behavioural outcome. After unilateral damage to the intrinsic neurons of the striatum, which includes GABAergic striatonigral projections, delayed trans-synaptic degeneration occurs in the ipsilateral substantia nigra pars reticulata (SNr). This degeneration was prevented by a 2-week regimen of muscimol delivered intraventricularly via osmotic minipumps. Muscimol is a direct-acting GABA agonist that presumably substituted for the absent GABA at the interface between the degenerating striatonigral GABAergic terminals and the GABAergic receptors located on SNr neurons. Sensorimotor asymmetry tests sensitive to unilateral striatal damage were carried out for 4 weeks to determine the functional consequences of the sparing of SNr neurons. Recovery of function was not improved. Instead, tactile extinction and hemiplegia were exaggerated in the contralateral forelimb. Other impairments were unaffected by the muscimol. The experiment was repeated using diazepam, rather than muscimol, to address the possibility that the disruptive effects of muscimol might reflect a more general disruptive influence on recovery processes. Diazepam, which has been shown in our lab to disrupt recovery of function after cortical lesions and to potentiate lesion-associated atrophy in remote subcortical structures, is an indirect-acting GABAergic agonist that requires GABA for its mechanism of action. Because GABAergic terminals at the SNr were destroyed, diazepam (as expected) failed to prevent SNr degeneration. Although diazepam presumably enhanced GABAergic synaptic activity in other brain regions, diazepam had no significant effect on postoperative behavioural function. Apparently, in the first experiment, the prevention of SNr degeneration per se was instrumental in the detrimental effects of muscimol. The rescued SNr neurons may have contributed to dysfunction because they lacked inhibitory GABAergic control. Transsynaptic degeneration secondary to brain damage was discussed as it might relate to release phenomena and their treatment by surgery or transmitter blocking agents in the clinical literature.

Animals↗

PubMed2006

Reduced functional activation after fatiguing exercise is not confined to primary motor areas.

We have previously shown that following a period of unimanual fatiguing exercise, there is a reduction in primary sensorimotor cortex (SM1) activation with movement of either the fatigued or the non-fatigued hand by Benwell et al. (Exp Brain Res 167:160-164, 2005). In the present study we have investigated whether this reduction is confined to motor areas or is more widespread. Functional imaging was performed before and after a 10-minute fatiguing exercise of the left hand (30% of maximum handgrip strength) in seven normal subjects (4 M, mean age 25 years). The activating task was a handgrip against a low resistance (1 kg) in response to a visual cue (chequerboard reversal every 2 +/- 0.5 s). We compared activation in SM1, supplementary motor area (SMA), cerebellum (CB) and primary visual cortex (V1) before and after the fatiguing exercise. After exercise, contralateral SM1 activation was reduced by 33% (P < 0.05) compared to baseline for the fatigued hand and by 49% for the non-fatigued hand (P < 0.05). A similar pattern was seen for the bilateral SMA and ipsilateral CB following exercise (45 vs. 50% for SMA; 30 vs. 35% for CB; fatigued versus non-fatigued). Activation was also reduced in V1 but to a lesser extent than in motor areas (19 vs. 24%; fatigued versus non-fatigued). These results show that although the reduced functional activation during the recovery period after fatiguing exercise is more marked in motor areas, it also extends to non-motor areas such as the visual cortex, suggesting that there are more widespread changes in cerebral haemodynamic responses after fatigue.

Adult↗

PubMed1986

Translation of sensory signals into commands for control of saccadic eye movements: role of primate superior colliculus.

Afferent signals that guide orienting movements converge in the deeper layers of the SC in a wide variety of animals. The sensory cells are arranged topographically according to their receptive-field locations and, thereby, form maps of sensory space. Maps of visual, somatosensory, and/or auditory space have been obtained in the iguana, mouse, hamster, barn owl, chinchilla, cat, and monkey. The deeper layers of the SC also contain neurons involved in the generation of movements of the eyes, head, vibrissae, and pinnae. Thus the SC, a site containing multiple sensory maps and perhaps multiple motor maps, has been selected by many investigators as a structure for investigating the problem of sensorimotor integration. In the mammalian nervous system, emphasized in this review, much remains to be learned about the structure, organization, and function of the SC. While anatomical studies continue to add to the knowledge of the sources of afferent projections, their pattern of laminar termination, and the source and destination of efferent projections, relatively little is known about the intrinsic organization of the colliculus, especially the deeper layers. Recently, electrophysiological studies have moved from an emphasis on the sensory and motor properties of collicular neurons to an examination of the maps of auditory and somatosensory space and the correspondence of these maps. In the future, major efforts aimed at identifying the functional properties of cells that project to the SC from diverse brain regions as well as the functional properties that project to the various structures receiving input from the colliculus are needed. A combination of anatomical and electrophysiological methods is required to describe the signal transforms that occur between the SC and motor areas (such as the paramedian pontine reticular formation) closer to the final common pathway. Conceptual and empirical work is needed to develop and test models of how the dynamic visual and auditory maps found in the primate SC are generated. In general, new and/or improved models of the role of the SC in sensorimotor integration are needed as guides for future research. A point of view emphasized here is that it may be fruitful to examine the function of the SC from a motor perspective. The nature of the motor command imposes constraints on the configuration of signals that can initiate movements and thereby determines the required transformation of sensory signals.

Acoustic Stimulation↗

PubMed2000

Regulation of rat cortex function by D1 dopamine receptors in the striatum.

Interactions between the basal ganglia and the cerebral cortex are critical for normal goal-directed behavior. In the present study, we used immediate-early genes (c-fos, zif 268) as functional markers to investigated how basal ganglia output altered by stimulation/blockade of D1 dopamine receptors in the striatum affects cortical function. Systemic administration of the mixed D1/D2 receptor agonist apomorphine (3 mg/kg) increased immediate-early gene expression in the striatum and throughout most of the cortex. Unilateral intrastriatal infusion of the selective D1 receptor antagonist SCH-23390 (0.5-10 microg) blocked this response bilaterally in striatum and cortex in a dose-dependent manner. Even apparently regionally restricted blockade of striatal D1 receptors attenuated gene expression throughout striatum and cortex in both hemispheres. Intrastriatal administration of the D1 antagonist inhibited apomorphine-induced sniffing/whisking, whereas other motor behaviors were unaffected. To determine whether such changes in cortical gene expression could reflect altered cortical function, we examined the effects of blocking striatal D1 receptors on whisker stimulation-evoked immediate-early gene expression in the sensorimotor cortex. Apomorphine increased sensory stimulation-evoked gene expression in the barrel cortex, and intrastriatal infusion of SCH-23390 attenuated this effect. These results suggest that stimulation of D1 dopamine receptors in the striatum exerts a widespread facilitatory effect on cortical function.

Animals↗

PubMed2000

Biochemical and neurobehavioral profile of CHF2819, a novel, orally active acetylcholinesterase inhibitor for Alzheimer's disease.

1,2,3,3a,8,8a-Hexahydro-1,3a,8-trimethylpyrrolo¿2,3-bĭndol-5-ol 2-ethylphenylcarbamate N-oxide hydrochloride (3aS-cis) (CHF2819) is a novel acetylcholinesterase inhibitor that produces central cholinergic stimulation after oral administration in rats. In vivo studies show that CHF2819 (0.5, 1.5, and 4.5 mg/kg p.o.) significantly increases acetylcholine levels in young adult rat hippocampus in a dose-dependent manner. Moreover, aged animals, which show a significant decrease in basal acetylcholine levels with respect to young adult rats, also exhibit a marked increase in the hippocampal concentrations of this neurotransmitter after the administration of CHF2819. This compound (1.5 mg/kg p.o.) significantly attenuates scopolamine-induced amnesia in a passive avoidance task. Furthermore, CHF2819 induces a significant decrease in dopamine levels and a significant elevation of extracellular concentrations of 5-hydroxytryptamine, whereas it does not modify norepinephrine and gamma-aminobutyric acid levels in the hippocampus of young adult rats. Functional observational battery screening demonstrates that CHF2819 (1.5 and 4.5 mg/kg p.o.) does not affect activity, excitability, autonomic, neuromuscular, and sensorimotor domains, as well as physiological end points (body weight and temperature). However, this compound induces involuntary motor movements (ranging from mild tremors to myoclonic jerks) in a dose-dependent manner. These findings suggest that the anti-amnestic properties of CHF2819, together with its stimulatory effect on cholinergic and serotonergic functions, might have a therapeutic potential mainly for the symptomatic treatment of Alzheimer's disease patients in which the cognitive impairment is accompanied by a depressive syndrome.

Acetylcholine↗

PubMed2002

The K-Cl cotransporter KCC3 is mutant in a severe peripheral neuropathy associated with agenesis of the corpus callosum.

Peripheral neuropathy associated with agenesis of the corpus callosum (ACCPN) is a severe sensorimotor neuropathy associated with mental retardation, dysmorphic features and complete or partial agenesis of the corpus callosum. ACCPN is transmitted in an autosomal recessive fashion and is found at a high frequency in the province of Quebec, Canada. ACCPN has been previously mapped to chromosome 15q. The gene SLC12A6 (solute carrier family 12, member 6), which encodes the K+-Cl- transporter KCC3 and maps within the ACCPN candidate region, was screened for mutations in individuals with ACCPN. Four distinct protein-truncating mutations were found: two in the French Canadian population and two in non-French Canadian families. The functional consequence of the predominant French Canadian mutation (2436delG, Thr813fsX813) was examined by heterologous expression of wildtype and mutant KCC3 in Xenopus laevis oocytes; the truncated mutant is appropriately glycosylated and expressed at the cellular membrane, where it is non-functional. Mice generated with a targeted deletion of Slc12a6 have a locomotor deficit, peripheral neuropathy and a sensorimotor gating deficit, similar to the human disease. Our findings identify mutations in SLC12A6 as the genetic lesion underlying ACCPN and suggest a critical role for SLC12A6 in the development and maintenance of the nervous system.

Agenesis of Corpus Callosum↗

PubMedDate not supplied

Immunotoxicological effects of JP-8 jet fuel exposure.

Chronic exposure to jet fuel has been shown to have adverse effects on human liver function, to cause emotional dysfunction, to cause abnormal electroencephalograms, to cause shortened attention spans, and to decrease sensorimotor speed (3-5). Due to the decision by the United States Air Force to implement the widespread use of JP-8 jet fuel in its operations, a thorough understanding of its potential effects upon exposed personnel is both critical and necessary. Exposure to potential environmental toxicants such as JP-8 may have significant effects on host systems beyond those readily visible (e.g., physiology, cardiology, respiratory, etc.); e.g., the immune system. Significant changes in immune consequences, even if short-lived, may have serious consequences for the exposed host that may impinge affect susceptibility to infectious agents. Major alterations in immune function that are long-lasting may result in an increased likelihood of development and/or progression of cancer, as well as autoimmune diseases. In the current study mice were exposed for 1h/day for 7 days to varying concentrations of aerosolized JP-8 jet fuel to simulate occupational exposures. Twenty-four hours after the last exposure the mice were analyzed for effects on their immune systems. It was observed that even at exposure concentrations as low as 100 mg/m3 detrimental effects on the immune system occurred. Decreases in viable immune cell numbers and immune organ weights were found. Jet fuel exposure resulted in losses of different immune cell subpopulations depending upon the immune organ being examined. Further, JP-8 exposure resulted in significantly decreased immune function, as analyzed by mitogenesis assays. Suppressed immune function could not be overcome by the addition of exogenous growth factors known to stimulate immune function. Thus, short-term, low concentration exposure of mice to JP-8 jet fuel caused significant toxicological effects on the immune system. It appears that the immune system may be the most sensitive indicator of toxicological damage due to JP-8 exposure, as effects were seen at concentrations of jet fuel that did not evidence change in other biological systems. Such changes may have significant effects on the health of the exposed individual.

Administration, Inhalation↗

PubMed1995

Nonocclusive common carotid artery thrombosis in the rat results in reversible sensorimotor and cognitive behavioral deficits.

BACKGROUND AND PURPOSE: Microemboli released during transient ischemic attack, stroke, and cardiac surgery are thought to cause a variety of functional deficits in humans. The purpose of this study was to characterize the type and extent of neurobehavioral deficits present after photochemically induced common carotid artery thrombosis (CCAT), a thromboembolic model of stroke in the rat that results in a platelet emboli shower. METHODS: Thirty-two male Wistar rats were assigned to four groups. Groups 1 (n = 8) and 3 (n = 8) were long-term (6-week survival) and short-term (2-week survival) experimental groups subjected to right CCAT with the use of the photochemical technique. Groups 2 (n = 8) and 4 (n = 8) served as sham-operated controls for each experimental group. A battery of behavioral tests was applied daily beginning 24 hours after thrombosis; this consisted of elicited forelimb placing, postural reflex, beam balance, beam walking, and open field activity. Cognitive testing with a water maze task was performed on post-CCAT days 30 to 33 for groups 1 and 2 and on post-CCAT day 2 for groups 3 and 4. Ten-micrometer coronal brain sections were stained with hematoxylin and eosin, and infarct location and frequency were determined. RESULTS: Significant sensorimotor deficits were observed, which recovered within 2 weeks after CCAT. The data that follow are derived by combining the two experimental groups and comparing these with the two sham groups. The following tests showed significant effects after CCAT: contralateral elicited forelimb placing, ipsilateral elicited forelimb placing, beam balance, and beam walking score. Cognitive dysfunction was seen acutely (group 3 animals) at 2 days after CCAT; Morris water maze length and latency to target were significantly greater in the experimental group. No deficits were seen in postural reflex, open field activity, or delayed cognitive testing. Histopathological assessment revealed small infarcts in 11 of 16 thrombosed rats. However, a strong relationship between neurobehavioral deficits and infarct location was not consistently demonstrated. CONCLUSIONS: CCAT produces consistent sensorimotor and cognitive behavioral deficits that recover within 2 weeks of injury. Behavioral outcome was not necessarily associated with overt histopathological damage, suggesting that reversible injury mechanisms, both vascular and neuronal, may be partly responsible for the temporary loss of function. These data strengthen the role of CCAT as a clinically relevant model of thromboembolic stroke.

Animals↗

PubMedDate not supplied

[Cortical plasticity and restoration of neurologic functions: an update on this topic].

INTRODUCTION: Neuroplasticity is a natural property of the nervous system to change its function and to reorganize due to a lesion or environmental changes. We review some of the main experimental and clinical experiences on cortical sensorimotor plasticity related to central nervous system (CNS) lesions. DEVELOPMENT: In the last 10 years increasing interest in neuronal plasticity has been prompted by several important discoveries. Long term potentiation and depression have been described as basic synaptic mechanism mediating functional recovery after CNS lesions, modulated by the up-down regulation of inhibitory-excitatory activity related to GABA, acetylcholine and glutamate between other neurotransmitters. In humans there are evidences from functional reorganization in the affected hemisphere in patients with hemispheric lesions, and the activation of homologues areas in the contralateral healthy hemisphere. Significative changes in the topography of cortical somatosensory and motor maps have been demonstrated using non invasive mapping techniques as multichannel EEG, evoked potential, transcranial magnetic stimulation, functional magnetic resonance imaging and positron emission tomography. Axonal and dendritic sprouting take place in animal models of brain lesions; but effective neural regeneration in the CNS does not seem to be a plausible mechanism for functional restoring. CONCLUSIONS: Plastic changes after CNS lesions make it possible the restoration of neurological functions in a high number of patients. It is important now to understand which changes are related to the clinical improvement of patients, and what might be done to promote or facilitate this changes and to inhibit maladaptive phenomena, for the design of rationale therapeutics strategies with modulatory influence on this process.

Amputation, Surgical↗

PubMed1985

Transplantation of embryonic ventral forebrain neurons to the neocortex of rats with lesions of nucleus basalis magnocellularis--II. Sensorimotor and learning impairments.

The cholinergic projection from the nucleus basalis magnocellularis to the neocortex has been implicated in normal memory function and in the dementia of Alzheimer's disease. In order to investigate functions of this cholinergic system of the forebrain, rats with unilateral ibotenic acid lesions of the nucleus basalis magnocellularis have been compared with normal animals and with rats given cortically-placed transplants, either of cholinergic-rich embryonic ventral forebrain cells or of control noncholinergic cells taken from embryonic hippocampus. In the first experiment, lesions of the nucleus basalis magnocellularis led to impairments in step-through passive avoidance and Morris' water-maze tasks, and to locomotor hyperactivity attributable to a reduction in within-trial habituation. The ventral forebrain grafts, but not the noncholinergic hippocampal grafts, significantly ameliorated the deficits of passive avoidance retention, and of water-maze spatial accuracy, but had no effect on the acquisition impairments in either task, nor on the habituation deficit in locomotor activity of the nucleus basalis magnocellularis lesioned rats. In the second experiment, the lesions induced contralateral sensory neglect and ipsilateral turning biases, which were also partially ameliorated by the ventral forebrain grafts. The results support the hypothesis that the basal forebrain-neocortical cholinergic system contributes to certain memory processes, but suggest a more general role for this system in other cortical functions also.

Animals↗

PubMed1984

[Influence of the sensorimotor cortex on single neurons of the nucleus gracilis in the cat].

The aim of this study was to investigate the functional role of the cortical projections to gracile nucleus. In unanesthetized cats single nuclear units projecting to the thalamus were tested for microstimulation of cortical foci (area 4) able to evoke single joint movements in contralateral hindlimb. A very significant percentage of gracile cells was influenced, very often in excitatory manner, if their receptive field was overlaying or very close to the joint controlled by a given cortical focus. Conversely, when the location of the receptive field was more distant, the percentage of responses and the incidence of excitatory effects decreased, inhibitions occurring more frequently. From a functional point of view, such an organization of the cortico-gracile control could be effective in modulating transmission of exteroceptive information from the region of the motor target (facilitation) as well as from adjacent ones (suppression). This arrangement could provide an higher resolution of afferent messages, in relation with the cortically induced movements.

Animals↗

PubMed2003

Model of recovery of locomotor ability after sensorimotor cortex injury in rats.

Animal models of locomotor recovery after brain injury provide tools for understanding the basic neurobiological processes that may underlie recovery after stroke in humans. Measurement of the ability of rats to traverse a narrow elevated beam has proven to be a particularly useful test of locomotor function. Repeated measurement of this behavior over time provides a simple method for quantifying the rate and degree of a rat's locomotor recovery after sensorimotor cortex injury and constitutes a tool for studying its mechanisms and possible treatment strategies. The model has proven particularly useful in predicting the effects of drugs on poststroke recovery in humans.

Animals↗

PubMedDate not supplied

Short-term exposure to JP-8 jet fuel results in long-term immunotoxicity.

Chronic exposure to jet fuel has been shown to have adverse effects on human liver function, to cause emotional dysfunction, to cause abnormal electroencephalograms, to cause shortened attention spans, and to decrease sensorimotor speed. Due to the decision by the United States Air Force to implement the widespread use of JP-8 jet fuel in its operations, a thorough understanding of its potential effects upon exposed personnel is both critical and necessary. Exposure to potential environmental toxicants such as JP-8 may have significant effects on host systems beyond those readily visible (i.e., physiology, cardiology, respiratory, etc.); e.g., the immune system. Previous studies have shown that short-term, low concentration JP-8 exposure had significant effects on the immune system, which should have serious consequences for the exposed host in terms of susceptibility to infectious agents. If these alterations in immune function were long-lasting, it might also result in an increased likelihood of development and/or progression of cancer, as well as autoimmune disease. In the current study, mice were exposed for 1 h/day for 7 days to a moderate (1000 mg/m3) and a high (2500 mg/m3) concentration of aerosolized JP-8 jet fuel to stimulate occupational exposures. One to 28 days after the last exposure the mice were analyzed for effects of the exposure on their immune systems. It was observed that decrease in viable immune cell numbers and immune organ weights found at 24 h after exposure persisted for extended periods of time. Further, JP-8 exposure resulted in significantly decreased immune infection, as analyzed by mitogenesis assays, which persisted for up to 4 weeks post-exposure. Thus, short-term exposure of mice to JP-8 jet fuel caused significant toxicological effects on the immune system, which were long-lasting and persistent. It appears that the immune system may be the most sensitive indicator of toxicological damage due to JP-8 exposure. Such long-term changes in immune status may have significant effects on the health of the exposed individual.

Aircraft↗

PubMed1998

Integrative visuomotor behavior is associated with interregionally coherent oscillations in the human brain.

Coherent electrical brain activity has been demonstrated to be associated with perceptual events in mammals. It is unclear whether or not it is also a mechanism instrumental in the performance of sensorimotor tasks requiring the continuous processing of information between primarily executive and receptive brain areas. In particular it is unknown whether or not interregional coherent activity detectable in electroencephalographic (EEG) recordings on the scalp reflects interareal functional cooperativity in humans. We studied patterns of changes in EEG-coherence associated with a visuomotor force-tracking task in seven subjects. Interregional coherence of EEG signals recorded from scalp regions overlying the visual and the motor cortex increased in comparison to a resting condition when subjects tracked a visual target by producing an isometric force with their right index finger. Coherence between visual and motor cortex decreased when the subjects produced a similar motor output in the presence of a visual distractor and was unchanged in a purely visual and purely motor task. Increases and decreases of coherence were best differentiated in the low beta frequency range (13-21 Hz). This observation suggests a special functional significance of low frequency oscillations in information processing in large-scale networks. These findings substantiate the view that coherent brain activity underlies integrative sensorimotor behavior.

Adult↗

PubMed1985

Microstimulation of the primate neostriatum. II. Somatotopic organization of striatal microexcitable zones and their relation to neuronal response properties.

Sensorimotor response properties of neostriatal neurons were characterized in conjunction with assessments of the motor effects of intrastriatal microstimulation in unanesthetized rhesus monkeys. Neuronal activity and microexcitability were assessed at 250- to 500-micron intervals and, in some cases, at 25- to 100-micron intervals. The results are based on the functional characterization of 878 putamen and 224 caudate neurons and analysis of the effects of microstimulation at each of these recording sites. Recording/stimulation sites were located between stereotaxic planes A6 and A22 in 81 microelectrode tracks from three monkeys. A total of 443 (50.4%) putamen neurons showed discrete responses to the sensorimotor examination. Of neurons with sensorimotor responses, 232 (52.4%) showed increased rates of discharge in relation to both active and passive movements of specific body parts. An additional 193 (43.6%) cells increased their rates of discharge only during the monkey's active movements of specific body parts. The remaining 18 (4.0%) cells appeared to respond exclusively to passive somatosensory stimulation. The sensorimotor response areas of putamen neurons ranged in size from an entire limb to a single joint. Putamen neurons were somatotopically organized throughout the rostrocaudal extent of the nucleus. Neurons with sensorimotor response areas involving the leg were located in the dorsolateral putamen, those with orofacial representations were located ventromedially, and those with arm representations were located in an intermediate position. Microstimulation evoked discrete movements of individual body parts at 21.6% of the 878 putamen sites. Over 95% (181/190) of the effective sites were located within the central half of the rostrocaudal extent of the putamen, between stereotaxic planes A10 and A17. The pattern of somatotopic organization revealed by microstimulation was the same as that derived from sensorimotor response properties of putamen neurons. Moreover, a close correspondence was observed between the movements evoked from a given SMZ and the functional properties of local neurons. In contrast to the results obtained in the putamen, none of the 224 stimulation sites in the caudate nucleus was microexcitable, and only 17 (7.6%) of the caudate neurons had definable sensorimotor response properties. This is consistent with the view that the primate putamen, by virtue of its anatomic connections with the sensorimotor and premotor cortical fields, is more directly involved in motor functions, whereas the caudate nucleus, by virtue of its connections with cortical "association" areas, is involved in more complex behavioral functions.

Animals↗