Ipsilateral motor responses of the facial muscles to intracortical microstimulation in the white mouse

Motor responses (MRs) of facial muscles to intracortical microstimulation (ICMS) of lightly anaesthetized outbred white mice were observed visually and recorded by means of photodiodes. ICMS rostral to bregma, within cortical band along sagittal suture (area 6) evoked mostly ipsilateral MRs of vibrissae and upper lip, more often from the left hemisphere. MRs of the lower jaw, tongue and larynx were induced by ICMS in symmetrical zones of both hemispheres. The lowest thresholds of ICMS, 2-20 mcA, were revealed at the depth from 0.8-1.1 mm up to 1.3-1.7 mm, i. e. in layers III and V. Short-latency (from 10 to 25 ms) MRs of the vibrissae, lip and jaw were evoked by high-frequency volleys of 2 to 5 pulses. The participation of some oligosynaptic components in cortico-facial descending projections in the white mouse is supposed.     

Motor responses of the facial muscles to local stimulation of the motor cortex and facial nerve nucleus in the white mouse

The character of motor responses of the facial muscles evoked by stimulation of various regions of the frontal neocortex and of the nucleus of the facial nerve was studied in outbred mice. Motor responses of the vibrissae, of the upper lip and the jaw to monopolar microstimulation in the frontal cortical areas in 55 per cent of the cases had the latencies from 5 to 15 ms. The latencies of the responses to the facial nucleus stimulation ranged from 3 to 12 ms with maximal expressed interval of 4-6 ms. Excitation conduction velocities of the facial nerve estimated on the basis of latencies measurements, were from 1.5 to 12 m/s.     

Orienting responses and vocalizations produced by microstimulation in the superior colliculus of the echolocating bat, Eptesicus fuscus

An echolocating bat actively controls the spatial acoustic information that drives its behavior by directing its head and ears and by modulating the spectro-temporal structure of its outgoing sonar emissions. The superior colliculus may function in the coordination of these orienting components of the bat's echolocation system. To test this hypothesis, chemical and electrical microstimulation experiments were carried out in the superior colliculus of the echolocating bat, Eptesicus fuscus, a species that uses frequency modulated sonar signals. Microstimulation elicited pinna and head movements, similar to those reported in other vertebrate species, and the direction of the evoked behaviors corresponded to the site of stimulation, yielding a map of orienting movements in the superior colliculus. Microstimulation of the bat superior colliculus also elicited sonar vocalizations, a motor behavior specific to the bat's acoustic orientation by echolocation. Electrical stimulation of the adjacent periaqueductal gray, shown to be involved in vocal production in other mammalian species, elicited vocal signals resembling acoustic communication calls of E. fuscus. The control of vocal signals in the bat is an integral part of its acoustic orienting system, and our findings suggest that the superior colliculus supports diverse and species-relevant sensorimotor behaviors, including those used for echolocation.     

Unit responses of the inferior colliculi to changes in the intensity of an amplitude-modulated signal

Unit responses of the inferior colliculi of anesthetized rats to amplitude-modulated sounds during a change in the carrier intensity were investigated. The following unit response characteristics were assessed: the number of spikes in the response, the range of reproduction of the modulation frequency, the response duration, and the pattern of the spike response relative to the envelope of the amplitude-modulated stimulus. The following parameters of the stimulus were varied: carrier intensity (usually of optimal frequency or noise), frequency of modulation (from 2 to 100 Hz), and carrier frequency. With a decrease in the intensity of the carrier in the case of monotonic neurons, and also with an increase or decrease in the intensity of the carrier relative to its optimal level in nonmonotonic neurons, the following changes in the discharge were regularly observed: the number of spikes in the response and its duration were reduced down to the appearance of only one initial response, the range of reproduction of the rhythm of modulation was narrowed, and the response pattern was sharply modified.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR. I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 5, No. 4, pp. 355–366, July–August, 1973.     

Unit responses in the "locomotor strip" of the cat hindbrain to microstimulation

Synaptic responses of single units in the "locomotor strip" of the hindbrain were recorded extracellularly. Short-latency responses appeared in neurons of the rostral part of the strip to stimulation of the "locomotor region" of the mesencephalon. Neurons of the caudal part of the strip responded to microstimulation of its other regions, including rostral. If the distance between the neuron and point of stimulation was under 2–3 mm, short-latency (1.2–1.6 msec) responses could be observed. The thresholds and latent periods of the responses increased when the distance apart increased. Polysynaptic responses with a latent period of 3–4 msec could be potentiated by an increase in the frequency of stimulation up to 30–40 Hz. It is suggested that axons of the "locomotor strip" are oriented in the rostrocaudal direction for a distance of 2–3 mm and give off collaterals which run toward neighboring neurons. The strip may be an integrative center, "intercalated" between the rostral portions of the brain stem and spinal cord.Deceased.Institute for Problems in Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 10, No. 5, pp. 510–518, September–October, 1978.     

Influence of long-term intracortical microstimulation on the motor cortex

Long-term (0.5–1 s) stimulation of the hand region of the motor cortex in both macaque and human through a microelectrode by a series of biphasic current pulses of small amplitude evokes different complex, coordinated movements of the hand. There are two different opinions on how these movements are produced. The first hypothesis associates the movements with the presence of specific subregions in the motor cortex, which reflect different ethologically relevant categories of movement. According to the second hypothesis, these evoked complex movements are the artifacts of electrical stimulation. This article discusses the results of a number of studies in favor of each of the hypotheses. The conclusion about the validity of the first hypothesis is based on the analysis of the results of microstimulation and their comparison with the data obtained by the latest methods without the use of electric current. Moreover, this finding suggests the possibility of testing the condition changes of the monkey motor cortex through analysis the characteristics of the movements caused by long-term microstimulation.     

The functional connections of the supraoptic and suprachiasmatic nuclei of the anterior hypothalamus with the superior colliculi

Interrelation of single hypothalamic (supraoptic--SO and suprachiasmatic--SCH nuclei) and light stimuli at the level of superior colliculus (SC) were studied during chronic experiments in waking rabbits. Short-term inhibitory and the subsequent facilitatory effects of the hypothalamic stimuli on SC responses induced by light flashes were established. The foregoing light stimulus caused inhibitory effect on formation of hypothalamo-collicular responses induced by SO and SCH nuclei stimulation. The final result of the anterior hypothalamic effect on SC function is the vector value of the mechanism of interrelation between the hypothalamic inputs in this structure.     

Interaction of recovery cycles of evoked potentials in the cerebral cortex of the cat in response to stimulation of the superior colliculi and pulvinar

Similar character of recovery cycles of evoked potentials in the visual cortex to electric stimulation of the superior colliculi (SC) and pulvinar was found in chronic experiments on alert cats irrespective of stimuli presentation order. In the association cortex preceding SC stimulation facilitated the response to test stimulation of pulvinar almost at all delays between the stimuli. If the pulvinar stimulation was applied as a conditioned stimulus, then the response to SC stimulation under intervals of 20-200 ms was depressed. The obtained data point to equivalence of the inputs from SC and pulvinar to the visual cortex, to different informational value of inputs from SC to the association and visual cortex, and to mutual function dependence of the inputs from SC and pulvinar to the association cortex.     

Influence of the motor cortex on lateral geniculate responses evoked in the cat by contralateral superior colliculus stimulation

It is shown that in nembutal anesthetized cats, a single stimulation of motor cortex (MC) causes a response in lateral geniculate nucleus (LGN). The development of this response had a conditioning effect on the LGN response evoked by stimulation of the contralateral superior colliculus (SC), markedly inhibiting it. The degree of this inhibition depended on the time interval between the cortical conditioning stimulation and the tectal test stimulation. A single conditioning MC stimulation did not noticeably change the LGN responses evoked by a light stimulus, but markedly inhibited visual responses from deep SC layers (those regions which on stimulation gave rise to LGN responses). From the results, it is suggested that the MC monitors the execution of tectal influences on LGN function at the tectal level rather than the geniculate level, and it is precisely by this means that it regulates saccadic suppression of LGN function, in the realization of which, as presumed earlier, the SC takes part.A. I. Karaev Institute of Physiology, Azerbaijan Academy of Sciences, Baku. Translated from Neirofiziologiya, Vol. 24, No. 4, July–August 1992.