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M F Jay

Publications and source records attributed to M F Jay.

4 recordsLinked to original sources
PubMed1987

Sensorimotor integration in the primate superior colliculus. I. Motor convergence.

Orienting movements of the eyes and head are made to both auditory and visual stimuli even though in the primary sensory pathways the locations of auditory and visual stimuli are encoded in different coordinates. This study was designed to differentiate between two possible mechanisms for sensory-to-motor transformation. Auditory and visual signals could be translated into common coordinates in order to share a single motor pathway or they could maintain anatomically separate sensory and motor routes for the initiation and guidance of orienting eye movements. The primary purpose of the study was to determine whether neurons in the superior colliculus (SC) that discharge before saccades to visual targets also discharge before saccades directed toward auditory targets. If they do, this would indicate that auditory and visual signals, originally encoded in different coordinates, have been converted into a single coordinate system and are sharing a motor circuit. Trained monkeys made saccadic eye movements to auditory or visual targets while the activity of visual-motor (V-M) cells and saccade-related burst (SRB) cells was monitored. The pattern of spike activity observed during trials in which saccades were made to visual targets was compared with that observed when comparable saccades were made to auditory targets. For most (57 of 59) V-M cells, sensory responses were observed only on visual trials. Auditory stimuli originating from the same region of space did not activate these cells. Yet, of the 72 V-M and SRB cells studied, 79% showed motor bursts prior to saccades to either auditory or visual targets. This finding indicates that visual and auditory signals, originally encoded in retinal and head-centered coordinates, respectively, have undergone a transformation that allows them to share a common efferent pathway for the generation of saccadic eye movements. Saccades to auditory targets usually have lower velocities than saccades of the same amplitude and direction made to acquire visual targets. Since fewer collicular cells are active prior to saccades to auditory targets, one determinant of saccadic velocity may be the number of collicular neurons discharging before a particular saccade.

Acoustic Stimulation↗
PubMed1987

Sensorimotor integration in the primate superior colliculus. II. Coordinates of auditory signals.

Based on the findings of the preceding paper, it is known that auditory and visual signals have been translated into common coordinates at the level of the superior colliculus (SC) and share a motor circuit involved in the generation of saccadic eye movements. It is not known, however, whether the translation of sensory signals into motor coordinates occurs prior to or within the SC. Nor is it known in what coordinates auditory signals observed in the SC are encoded. The present experiment tested two alternative hypotheses concerning the frame of reference of auditory signals found in the deeper layers of the SC. The hypothesis that auditory signals are encoded in head coordinates predicts that, with the head stationary, the response of auditory neurons will not be affected by variations in eye position but will be determined by the location of the sound source. The hypothesis that auditory responses encode the trajectory of the eye movement required to look to the target (motor error) predicts that the response of auditory cells will depend on both the position of the sound source and the position of the eyes in the orbit. Extracellular single-unit recordings were obtained from neurons in the SC while monkeys made delayed saccades to auditory or visual targets in a darkened room. The coordinates of auditory signals were studied by plotting auditory receptive fields while the animal fixated one of three targets placed 24 degrees apart along the horizontal plane. For 99 of 121 SC cells, the spatial location of the auditory receptive field was significantly altered by the position of the eyes in the orbit. In contrast, the responses of five sound-sensitive cells isolated in the inferior colliculus were not affected by variations in eye position. The possibility that systematic variations in the position of the pinnae associated with different fixation positions could account for these findings was controlled for by plotting auditory receptive fields while the pinnae were mechanically restrained. Under these conditions, the position of the eyes in the orbit still had a significant effect on the responsiveness of collicular neurons to auditory stimuli. The average magnitude of the shift of the auditory receptive field with changes in eye position (12.9 degrees) did not correspond to the magnitude of the shift in eye position (24 degrees). Alternative explanations for this finding were considered. One possibility is that, within the SC, there is a gradual transition from auditory signals in head coordinates to signals in motor error coordinates.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗
PubMedDate not supplied

Auditory receptive fields in primate superior colliculus shift with changes in eye position.

The process by which sensory signals are transformed into commands for the control of movement is poorly understood. A potential site for such a transformation is the superior colliculus (SC), which receives auditory, visual and somatosensory inputs and contains neurones that discharge before saccadic eye movements. Along the primary sensory pathways, signals coding the spatial location of auditory, visual and somatosensory targets are based on distinctly different coordinate systems, and it is not known whether each type of sensory input uses a separate motor pathway or if they are converted into a common coordinate system in order to share a single pre-motor circuit. Sensory neurones in the SC have spatially restricted receptive fields (RFs) and are organized into maps across the collicular surface. Acute experiments have shown a rough correspondence between the spatial positions of RFs of neurones encountered along a single dorsal-ventral penetration of the colliculus, regardless of the modality of the effective stimulus, suggesting that auditory, visual and somatosensory maps might be in register. However, in these conditions the head-centred auditory system and the retinotopic visual system are aligned because the eyes are in the primary orbital position. Moreover, other data have suggested that the primate SC is organized in motor, not sensory, coordinates, although in the cat, eye position was found to have no effect on auditory receptive fields. We therefore sought here to determine what happens to the registration of the auditory and visual maps in the alert, behaving animal. Monkeys, with heads fixed, were trained to make delayed saccadic eye movements to auditory or visual targets from one of three initial fixation points while the activity of single neurones was recorded extracellularly. We found that the auditory receptive fields shifted with changes in eye position, allowing the auditory and visual maps to remain in register.

Acoustic Stimulation↗