Two-dimensional spatiotemporal coding of linear acceleration in vestibular nuclei neurons.

Response properties of vertical (VC) and horizontal (HC) canal/otolith-convergent vestibular nuclei neurons were studied in decerebrate rats during stimulation with sinusoidal linear accelerations (0.2-1.4 Hz) along different directions in the head horizontal plane.

Contribution of irregular semicircular canal afferents to the horizontal vestibuloocular response during constant velocity rotation.

1. The effects of constant anodal currents (100 microA) delivered bilaterally to both labyrinths on the horizontal vestibuloocular response (VOR) were studied in squirrel monkeys during steps of angular velocity in the dark. We report that bilateral anodal currents decreased eye velocity approximately 30-50% during the period of galvanic stimulation without a change in the time constant of VOR.

Angular velocity detection by head movements orthogonal to the plane of rotation.

Sinusoidal oscillation of rhesus monkeys about a head-fixed, earth-horizontal axis while rotating at constant velocity about an earth-vertical axis generates a characteristic ocular nystagmus where the three-dimensional slow phase eye velocity is compensatory to the spatially and temporally changing head angular velocity vector. This includes the generation of a unidirectional nystagmus characterised by a "bias" slow phase velocity component, albeit of small gain (0.2-0.

Spatial and temporal coding in single neurons.

Convergence between cells which differ in both spatial and temporal properties create higher order neurons with response properties that are distinctly different from those of the input neurons. The spatial properties of target neurons are not necessarily "cosine-tuned". In addition, unlike the independence between spatial and temporal properties in cosine-tuned afferent neurons, higher-order target cells generally exhibit a dependence of temporal dynamics on spatial properties.

Modelling spatiotemporal properties of directionally sensitive multi-input single-output systems.

The dynamics of directionally tuned linear multi-input single-output systems varies generally as a function of the spatial orientation of the inputs. A linear system receiving directionally specific inputs is represented by a linear combination of the respective input transfer functions. The input-output behaviour of such systems can be described by a vector transfer function which specifies the polarization directions of the system in real space.

Non-uniform temporal scaling of hand and finger kinematics during typing.

We examined the manner in which the keystroke kinematics of the hand and the fingers varied with the mean rate of typing by trained typists. We used words and phrases in which only one letter was typed with the right hand and all of the remaining letters were typed using the left hand. We varied the typing rate over a threefold range (intervals between keypresses ranging from 150 ms to 500 ms) with the aid of a metronome.

Role of irregular otolith afferents in the steady-state nystagmus during off-vertical axis rotation.

1. During constant velocity off-vertical axis rotations (OVAR) in the dark a compensatory ocular nystagmus is present throughout rotation despite the lack of a maintained signal from the semicircular canals. Lesion experiments and canal plugging have attributed the steady-state ocular nystagmus during OVAR to inputs from the otolith organs and have demonstrated that it depends on an intact velocity storage mechanism.

Spatio-temporal convergence (STC) in otolith neurons.

It has been recently demonstrated that some primary otolith afferents and most otolith-related vestibular nuclei neurons encode two spatial dimensions that can be described by two vectors in temporal and spatial quadrature. These cells are called broadly-tuned neurons. They are characterized by a non-zero tuning ratio which is defined as the ratio of the minimum over the maximum sensitivity of the neuron.

A model for the characterization of the spatial properties in vestibular neurons.

Quantitative study of the static and dynamic response properties of some otolith-sensitive neurons has been difficult in the past partly because their responses to different linear acceleration vectors exhibited no "null" plane and a dependence of phase on stimulus orientation. The theoretical formulation of the response ellipse provides a quantitative way to estimate the spatio-temporal properties of such neurons. Its semi-major axis gives the direction of the polarization vector (i.

Detection of rotating gravity signals.

It is shown in the preceding paper that neurons with two-dimensional spatio-temporal properties to linear acceleration behave like one-dimensional rate sensors: they encode the component of angular velocity (associated with a rotating linear acceleration vector) that is normal to their response plane. During off-vertical axis rotation (OVAR) otolith-sensitive neurons are activated by the gravity vector as it rotates relative to the head. Unlike "one-dimensional" linear accelerometer neurons which exhibit equal response magnitudes for both directions of rotation, "two-dimensional" neurons can be shown to respond with unequal magnitudes to clockwise and counterclockwise off-vertical axis rotations.

Two-dimensional coding of linear acceleration and the angular velocity sensitivity of the otolith system.

There exist otolith-sensitive vestibular nuclei neurons with spatio-temporal properties that can be described by two response vectors that are in temporal and spatial quadrature. These neurons respond to the component of a stimulus vector on a plane rather than a single axis. It is demonstrated here that these "two-dimensional" linear accelerometer neurons can function as one-dimensional angular velocity detectors.

Dynamic polarization vector of spatially tuned neurons.

The study of the dynamic properties of otolith neurons has been difficult previously because of the differing response sensitivities of individual cells to specific stimulus directions and the lack of a general mathematical scheme that could explain and account for all their response features. The present paper describes a method for estimating both the spatial and temporal properties of neurons like the otolith neurons that are spatially tuned to different stimulus directions. At each stimulus frequency, a response elipse can be constructed from the neural responses elicited by stimulation along three linear independent axes.

Response properties of gerbil otolith afferents to small angle pitch and roll tilts.

The responses from isolated single otolith afferent fibers were obtained to small angle sinusoidal pitch and roll tilts in anesthetized gerbils. The stimulus directions that produced the maximum (response vector) and minimum response sensitivities were determined for each otolith afferent, with response vectors for the units being spread throughout the horizontal plane, similar to those reported for other species. A breadth of tuning measure was derived, with narrowly tuned neurons responding maximally to stimulation in one direction and minimally along an orthogonal ('null') direction.

The vestibulo-ocular reflex in the cat during linear acceleration in the sagittal plane.

The horizontal and vertical components of the vestibulo-ocular reflex (VOR) were recorded in alert cats that were rotated with their head placed on or 45 cm eccentric from the axis of rotation. During off-axis rotation there was a centripetal acceleration along the animal's naso-occipital axis that changed the direction and the magnitude of the resultant otolith force in the animal's sagittal plane. When the animal was upright and eccentric from the axis of rotation, the horizontal VOR (HVOR) had a shorter time constant and smaller amplitude compared to the on-axis HVOR.

Models of membrane resonance in pigeon semicircular canal type II hair cells.

Pigeon vestibular semicircular canal type II hair cells often exhibit voltage oscillations following current steps that depolarize the cell membrane from its resting potential. Currents active around the resting membrane potential and most likely responsible for the observed resonant behavior are the Ca(++)-insensitive, inactivating potassium conductance IA (A-current) and delayed rectifier potassium conductance IK. Several equivalent circuits are considered as representative of the hair cell membrane behavior, sufficient to explain and quantitatively fit the observed voltage oscillations.

The horizontal vestibulo-ocular reflex during linear acceleration in the frontal plane of the cat.

Horizontal and vertical eye movements were recorded in alert, restrained cats that were subjected to whole-body rotations with the horizontal semicircular canals in the plane of rotation and the body centered on the axis or 45 cm eccentric from the axis of rotation. Changes in the horizontal vestibulo-ocular reflex (HVOR) due to the resultant of the linear forces (i.e.

Changes in the dynamics of the vertical vestibulo-ocular reflex due to linear acceleration in the frontal plane of the cat.

The vertical and horizontal components of the vestibulo-ocular reflex (VOR) were recorded in alert, restrained cats who were placed on their sides and subjected to whole-body rotations in the horizontal plane. The head was either on the axis or 45 cm eccentric from the axis rotation. During off-axis rotation there was a change in the linear force acting on the otolith organs due to the presence of a centripetal acceleration along the animal's vertical axis.