Activity of cat premotor cortex neurons during visually guided stepping.

Visual control of steps is critical in everyday life. Several motor centers are implicated in visual control of steps on a complex surface, however, participation of a large cortical motor area, the premotor cortex, in visual guidance of steps during overground locomotion has not been examined. Here, we analyzed the activity of neurons in feline premotor cortex areas 6aα and 6aγ as cats walked on the flat surface where visual guidance of steps is not needed and stepped on crosspieces of a horizontally placed ladder or over barriers where visual control of steps is required.

Signals from posterior parietal area 5 to motor cortex during locomotion.

Area 5 of the parietal cortex is part of the "dorsal stream" cortical pathway which processes visual information for action. The signals that area 5 ultimately conveys to motor cortex, the main area providing output to the spinal cord, are unknown. We analyzed area 5 neuronal activity during vision-independent locomotion on a flat surface and vision-dependent locomotion on a horizontal ladder in cats focusing on corticocortical neurons (CCs) projecting to motor cortex from the upper and deeper cortical layers and compared it to that of neighboring unidentified neurons (noIDs).

Contribution of the ventrolateral thalamus to the locomotion-related activity of motor cortex.

The activity of motor cortex is necessary for accurate stepping on a complex terrain. How this activity is generated remains unclear. The goal of this study was to clarify the contribution of signals from the ventrolateral thalamus (VL) to formation of locomotion-related activity of motor cortex during vision-independent and vision-dependent locomotion.

Low intensity vibration of ankle muscles improves balance in elderly persons at high risk of falling.

In our study we examined postural performance of young healthy persons (HY), elderly healthy persons (HE), and elderly persons at high risk of falling (FR). Anterio-posterior (AP) and medio-lateral (ML) ankle and hip angular deviations, as well as linear displacements of the center of mass (COM) were assessed in persons standing with eyes either open or closed, while none, and 40 and 30 Hz vibrations were applied bilaterally to the ankle muscle gastrocnemius. During quiet standing with eyes open, balance parameters in FR group differed from those in healthy groups.

The influence of mechanical vibration on local and central balance control.

Fall prevention has an indispensable role in enhancing life expectancy and quality of life among older adults. The first step to prevent falls is to devise reliable methods to identify individuals at high fall risk. The purpose of the current study was to assess alterations in local postural muscle and central sensory balance control mechanisms due to low-frequency externally applied vibration among elders at high fall risk, in comparison with healthy controls, as a potential tool for assessing fall risk.

Strategies for obstacle avoidance during walking in the cat.

Avoiding obstacles is essential for successful navigation through complex environments. This study aimed to clarify what strategies are used by a typical quadruped, the cat, to avoid obstacles during walking. Four cats walked along a corridor 2.

Head movement during walking in the cat.

Knowledge of how the head moves during locomotion is essential for understanding how locomotion is controlled by sensory systems of the head. We have analyzed head movements of the cat walking along a straight flat pathway in the darkness and light. We found that cats' head left-right translations, and roll and yaw rotations oscillated once per stride, while fore-aft and vertical translations, and pitch rotations oscillated twice.

Burst firing of neurons in the thalamic reticular nucleus during locomotion.

This study examined the burst firing of neurons in the motor sector of the thalamic reticular nucleus (RE) of the cat. These neurons are inhibitory cells that project to the motor thalamus. The firing activity of RE neurons was studied during four behaviors: sleep, standing, walking on a flat surface, and accurate stepping on crosspieces of a horizontal ladder.

Differential gating of thalamocortical signals by reticular nucleus of thalamus during locomotion.

The thalamic reticular nucleus (RE) provides inhibition to the dorsal thalamus, and forms a crucial interface between thalamocortical and corticothalamic signals. Whereas there has been significant interest in the role of the RE in organizing thalamocortical signaling, information on the activity of the RE in the awake animal is scant. Here we investigated the activity of neurons within the "motor" compartment of the RE in the awake, unrestrained cat during simple locomotion on a flat surface and complex locomotion along a horizontal ladder that required visual control of stepping.

Signals from the ventrolateral thalamus to the motor cortex during locomotion.

The activity of the motor cortex during locomotion is profoundly modulated in the rhythm of strides. The source of modulation is not known. In this study we examined the activity of one of the major sources of afferent input to the motor cortex, the ventrolateral thalamus (VL).

Self-motion signals in vestibular nuclei neurons projecting to the thalamus in the alert squirrel monkey.

Sixty vestibular nuclei neurons antidromically activated by electrical stimulation of the ventroposterior thalamus were recorded in two alert squirrel monkeys. The majority of these neurons were monosynaptically activated by vestibular nerve electrical stimulation. Forty-seven neurons responded to animal rotations around the earth-vertical axis; 16 of them also responded to translations in the horizontal plane.

Coding of self-motion signals in ventro-posterior thalamus neurons in the alert squirrel monkey.

The firing behavior of 47 ventro-posterior thalamus neurons was studied in two alert squirrel monkeys during rotations of whole body, head and trunk. A total of 27 of these neurons (57%) were sensitive to spatial motion of the head irrespective of the mode of motion. These neurons responded similarly when the head moved simultaneously with the trunk, and when the head voluntarily or involuntarily moved on the stationary trunk.

Activity of ventroposterior thalamus neurons during rotation and translation in the horizontal plane in the alert squirrel monkey.

The firing behavior of 107 vestibular-sensitive neurons in the ventroposterior thalamus was studied in two alert squirrel monkeys during whole body rotation and translation in the horizontal plane. Vestibular-sensitive neurons were distributed primarily along the anterior and posterior borders of ventroposterior nuclei; three clusters of these neurons could be distinguished based on their location and inputs. Eighty-four neurons responded to rotation; 66 (78%) of them responded to rotation only and 18 (22%) to both rotation and translation.

Efferent-mediated fluctuations in vestibular nerve discharge: a novel, positive-feedback mechanism of efferent control.

We compared the background discharge of vestibular nerve afferents in barbiturate-anesthetized and unanesthetized, decerebrate chinchillas. Based on their interspike-interval statistics, units were categorized as regular, intermediate, or irregular. Background discharge rates were higher in irregular units from decerebrates compared to anesthetized preparations; no such difference was observed for regular or intermediate units.

Efferent actions in the chinchilla vestibular labyrinth.

Efferent fibers were electrically stimulated in the brain stem, while afferent activity was recorded from the superior vestibular nerve in barbiturate-anesthetized chinchillas. We concentrated on canal afferents, but otolith afferents were also studied. Among canal fibers, calyx afferents were recognized by their irregular discharge and low rotational gains.

Reflections of efferent activity in rotational responses of chinchilla vestibular afferents.

To study presumed efferent-mediated responses, we determined if afferents responded to head rotations that stimulated semicircular canals other than the organ being innervated. To minimize stimulation of an afferent's own canal, its plane was placed nearly orthogonal to the rotation plane. Otolith units were tested in a horizontal head position with the ear placed near the rotation axis to minimize linear forces.