Vladimir Marlinski

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. Forty-one neurons were sensitive to linear translation; 23 (56%) of them responded to translation only. The population rotational response to 0.5-Hz sinusoids with a peak velocity of 40 degrees /s showed a gain of 0.23 +/- 0.15 spike.s(-1).deg(-1).s(-1) and phase lagging behind the angular velocity by -9.3 +/- 34.1 degrees . Although rotational response amplitude increased with the stimulus velocity across the range 4-100 degrees /s, the rotational sensitivity decreased with and was inversely proportional to the stimulus velocity. The rotational response amplitude and sensitivity increased with the stimulus frequency across the range 0.2-4.0 Hz. The population response to sinusoidal translation at 0.5 Hz and 0.1 g amplitude had a gain of 111.3 +/- 53.7 spikes.s(-1).g(-1) and lagged behind stimulus acceleration by -71.9 +/- 42.6 degrees . Translational sensitivity decreased as acceleration increased and this was inversely proportional to the square root of the acceleration. Results of this study imply that changes in the discharge rate of vestibular-sensitive thalamic neurons can be approximated using power functions of the angular and linear velocity of spatial motion.

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. The mean sensitivity to 0.5-Hz rotations of 80 degrees /s velocity was 0.40 +/- 0.31 spikes.s(-1).deg(-1).s(-1). Rotational responses were in phase with stimulus velocity. Sensitivities to 0.5-Hz translations of 0.1 g acceleration varied from 92.2 to 359 spikes.s(-1).g(-1) and response phases varied from 10.1 degrees lead to -98 degrees lag. The firing behavior in 28 neurons was studied during rotation of the whole animal, of the trunk, and voluntary and involuntary rotations of the head. Two classes of vestibulothalamic neurons were distinguished. One class of neurons generated signals related to movement of the head that were similar either when the head and trunk move together or when the head moves on the stationary trunk. A fraction of these neurons fired during involuntary head movements only. A second class of neurons generated signals related to movement of the trunk. They responded when the trunk moved alone or simultaneously with the head, but did not respond to head rotations while the trunk was stationary.

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). Experiments were conducted in chronically implanted cats with an extracellular single-neuron recording technique. VL neurons projecting to the motor cortex were identified by antidromic responses. During locomotion, the activity of 92% of neurons was modulated in the rhythm of strides; 67% of cells discharged one activity burst per stride, a pattern typical for the motor cortex. The characteristics of these discharges in most VL neurons appeared to be well suited to contribute to the locomotion-related activity of the motor cortex. In addition to simple locomotion, we examined VL activity during walking on a horizontal ladder, a task that requires vision for correct foot placement. Upon transition from simple to ladder locomotion, the activity of most VL neurons exhibited the same changes that have been reported for the motor cortex, i.e., an increase in the strength of stride-related modulation and shortening of the discharge duration. Five modes of integration of simple and ladder locomotion-related information were recognized in the VL. We suggest that, in addition to contributing to the locomotion-related activity in the motor cortex during simple locomotion, the VL integrates and transmits signals needed for correct foot placement on a complex terrain to the motor cortex.

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. These neurons did not respond to rotation of the trunk when the spatial position of the head was fixed. Five neurons (11%) responded only to involuntary movement of the head produced by external force, but were insensitive to voluntary spatial head movement. They also did not respond to spatial motion of the trunk. Totally 15 neurons (32%) were sensitive to spatial motion, which included rotation of the trunk. These neurons responded when the trunk moved alone, and when the trunk moved simultaneously with the head, but were not responsive to spatial movement of the head while the trunk was stationary. We suggest that the vestibulo–thalamo–cortical pathway comprises two distinct functional channels. In one of these channels, cephalokinetic, spatial motion of the head is coded. In the other channel, somatokinetic, motion of the body in space is coded. Each of these channels further consists of two divisions. In the principal division the motion signal is conveyed continuously, irrespective of the behavioral context of motion. In the other auxiliary division the signal only codes movement caused by externally applied force.