Electromyographic and motor cortical responses to imposed displacements of the cat elbow: disparities and homologies with those of the primate wrist.
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Animals↗
Biomedical subjects
I C Bruce
Publications and source records attributed to I C Bruce.
Descending projections to the cervical spinal cord in the developing kitten.
The distribution of neurons filled by retrograde axonal transport of horseradish peroxidase from the cervical enlargement is described in kittens prior to and following the time of appearance of mature alpha-motoneuron responses to motor cortical stimulation (at 107-111 days gestational age; about 41 days postnatally). Cortex and brainstem reconstructions of the distributions of filled neurons demonstrate a well-defined, discrete projection from cortical area 4 to spinal cord segments C3 to C8, both in mature and immature (20 and 24 days postnatal) animals. In addition, appropriate rubrospinal, reticulospinal and vestibulospinal projections were present at all ages studied.
Animals↗
Comment: a schema for the interactions between motor programs and sensory input.
In this overview we utilize and extend a model, originally developed for "command interneuron" control of the generation of motor programs, to discuss the roles sensory inputs play in movement control. To provide a conceptual framework, we present a modular schematic of the motor control and sensory processing apparatus of an hypothetical nervous system. In the schematic, "subroutines" (basic units of motor programs) are seen as "playing out" through switching and sequencing networks to "driver neurons." The "driver neurons" then activate motoneurons to execute the programmed movements. Five modes of interaction between motor programs and sensory input are considered using examples from invertebrate and vertebrate neuronal circuitry. These modes of interaction occur at the following locations: (1) the "program selector," to initiate a motor program; (2) the "motor subroutine directory," advancing the program to the next subroutine; (3) the "driver neurons" and motoneurons, where the "gain" of subroutine instructions can be modulated; (4) the "motor programmer," which monitors programs in progress and provides for program development and updating; and (5) the "driver neurons" themselves, which control sensory processing by "selecting" the appropriate sensory inputs for the program in progress. Mode 5 is illustrated in more detail through a consideration of the modification of stretch receptor input by "extensor" and "flexor" command interneurones in the circuitry controlling postural movements of the crayfish abdomen.
Humans↗
Synchronous development of motor cortical output to different muscles in the kitten.
Previous observations indicate that the output linkages from motor cortex (area 4) to triceps brachii motoneurons develop relatively late in the postnatal kitten. Responses in multiple, simultaneously-recorded EMG's from facial, forelimb and proximal hindlimb musculature to intracortical microstimulation appear over gestational days 107-111 (about 41 days postnatally). Thus, output from the motor cortex to alpha motoneurons develops in a synchronous, rather than a sequential manner across the area 4 homunculi.
Aging↗
Sequential output-input maturation of kitten motor cortex.
Average response histograms of the responses of single cortical neurons to imposed forelimb displacements in the kitten were utilized to quantify: (1) Background activity, (2) excitatory response latency, (3) percentage responding neurons, and (4) synaptic effectiveness. Motor cortical neuronal responses to the input did not attain adult values until 55--65 days of age, while adult-like responses were found in somatosensory cortical neurons as early as 9 days postnatally. Motor cortical output to alpha-motoneurons innervating triceps brachii, as tested by intracortical and subcortical microstimulation, first appeared over an interval ranging from 37--45 days postnatally. Thus, motor cortical responses to forelimb mechanoreceptors develop after completion of the output linkages from motor cortex to forelimb motoneurons and, though the motor cortex can output at 45 days, motor cortical functions requiring somatosensory feedback cannot be operative until about 60 days. This system provides a discrete and "late" maturing model in which to study the postnatal development of neuronal networks underlying normal and abnormal motor behavior.
Afferent Pathways↗
Functional development of motor cortical neurones in the kitten [proceedings].
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Animals↗
Renewal-process approximation of a stochastic threshold model for electrical neural stimulation.
In a recent set of modeling studies we have developed a stochastic threshold model of auditory nerve response to single biphasic electrical pulses (Bruce et al., 1999c) and moderate rate (less than 800 pulses per second) pulse trains (Bruce et al., 1999a). In this article we derive an analytical approximation for the single-pulse model, which is then extended to describe the pulse-train model in the case of evenly timed, uniform pulses. This renewal-process description provides an accurate and computationally efficient model of electrical stimulation of single auditory nerve fibers by a cochlear implant that may be extended to other forms of electrical neural stimulation.
Action Potentials↗
Reversal of long-latency reflexes in first dorsal interosseous during a force-tracking task.
Cutaneous reflexes in response to electrical stimulation of the index finger were recorded from first dorsal interosseous (1DI) at specified force levels under three conditions: during a static posture and during the incremental and decremental phases of a sinusoidal, force-tracking task. Under static conditions, while 1DI generated a steady force [10, 20 or 30% maximum voluntary contraction (MVC)], four reflex components could be identified: E1, I1, E2 and I2. The amplitudes of these components were measured as the subjects tracked a 0.5 Hz sine wave by gradually changing the force output of 1DI between zero and 40% MVC. E1 and I1 showed minimal changes from the static condition, while activity during the E2 period was inhibitory during the incremental phase and excitatory during the decremental phase of tracking. Abrupt switching from inhibition to excitation during the E2 period occurred around the transition from incremental to decremental force. Activity during the I2 period was less markedly modulated than that during E2. Reflex reversal during the E2 interval may function to reduce the rate of change of force under conditions requiring precise force-control.
Adolescent↗
Electromyographic activity in a distant muscle during simple voluntary movements: an unexpected hand-eye linkage.
PURPOSE: Supraspinal sensorimotor maps contain adjacent representations of the hand and face. These experiments were designed to determine whether interactions between the representations could be detected at the periphery. METHODS: Simultaneous EMG recordings were made from orbicularis oculi and wrist flexor during three conditions, with 50 repetitions each: during exposure to an auditory cue; responding to the auditory cue by wrist flexion; and performing a self-paced wrist flexion in the absence of an auditory cue. RESULTS: In 8 of 10 healthy volunteers, the rectified, averaged EMGs showed small but consistent increases in orbicularis oculi activity during wrist flexion in the two tasks involving that movement, but not in the auditory task alone. CONCLUSION: In one or more of the central sensorimotor maps, voluntary activation of the wrist flexor representation is accompanied by liminal activation of a nearby facial representation which projects to the motoneurons of orbicularis oculi.
Acoustic Stimulation↗