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A Boddy

Publications and source records attributed to A Boddy.

22 records · Page 2Linked to original sources
PubMed1988

Afferent signals from cat extraocular muscles in the medial vestibular nucleus, the nucleus praepositus hypoglossi and adjacent brainstem structures.

The responses of single units in the vestibular nuclei, nucleus praepositus hypoglossi and in the brainstem, deep and posterior to the abducens nucleus, were studied in anaesthetized, paralysed cats. Natural vestibular stimulation was provided by horizontal, sinusoidal oscillation of the animal and extraocular muscle afferents of the ipsilateral eye were activated either by passive eye-movement or by electrical stimulation of the inferior oblique branch of the oculomotor nerve in the orbit. Unit responses to vestibular and/or orbital stimuli were examined in sets of peristimulus time histograms interleaved in time. Of 127 units exposed to both types of stimulus, 40 (32%) responded only to vestibular input; 46 (32%) were affected only by the orbital afferent signal and 19 (15%) received both signals; the remaining 22 units (17%) were discarded because they had polymodal (usually somaesthetic) input. Of the 93 units whose recording sites were determined histologically, 24 were in the medial vestibular nucleus, 16 in the n. praepositus hypoglossi and 45 in the magnocellular nucleus of the reticular formation posterior and deep to the abducens nucleus. In these three nuclei 19 units in total were found which carried the orbital proprioceptive afferent signal and also responded to horizontal vestibular stimulation. The input from the eye muscles proved able to modify the vestibular response by adding excitation or inhibition or both. Effects of the orbital signal were generally phasic. About half of the units which responded to passive eye-movement showed statistically significant differences between their responses to horizontal and to vertical eye-movement. We have shown previously that signals from extraocular muscle proprioceptors reach the vestibulo-oculomotor system in an amphibian and a bony fish; the present experiments show that this is the case in a mammal also. The fact that the visual and visuomotor behaviour of these three species is very different suggests that the proprioceptive signal may play some rather fundamental role in the vestibulo-ocular system. The principal interest of the present results is that they demonstrate that units in the central vestibular system of the cat, in structures which are known to be concerned in oculomotor control, and particularly in the organization of horizontal eye-movement, receive an afferent signal from the eye muscles during passive eye-movement. These brainstem nuclei are known to receive various combinations of input from the vestibular and visual systems and of signals which represent neck movement and eye position and velocity.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1984

Input from proprioceptors in the extrinsic ocular muscles to the vestibular nuclei in the giant toad, bufo marinus.

Extracellular unit records were made from the left brain stem of decerebrate, paralysed giant toads (Bufo marinus) during passive movement of the ipsilateral eye. Units in the vestibular nuclear complex (VN) were identified by their short-latency responses to electrical stimulation of the anterior branch of the ipsilateral VIII cranial nerve. Of 58 units in the region of VN, as judged from field potentials to VIII nerve stimulation, fourteen gave phasic excitatory responses to passive movement of the eye and were also identified as vestibular nuclear units. A further twelve units which responded to eye-movement could not be assigned to VN; the remaining 32 units were in VN but did not respond to passive eye-movement. Also, of 16 units whose recording sites were identified histologically in the VN complex, 11 gave responses to vestibular nerve stimulation and to passive eye-movement and 5 responded to eye-movement only. Control experiments eliminated auditory, visual and cutaneous sources for the signal produced by passive eye-movement; thus, the signal must have arisen from intraorbital proprioceptors. Units in VN were also found which were excited by electrical stimulation of the intraorbital part of the fourth (trochlear) nerve; this provides strong evidence that proprioceptors in the extrinsic ocular muscles (EOM) are included in the receptors which provide the signal to VN during passive eye-movement. The effects of vestibular stimulation and of passive eye-movement were found to interact upon units in VN. When passive eye-movement and vestibular stimulation were paired the response to the second stimulus was significantly reduced over a range of interstimulus intervals. The conclusions are that orbital proprioceptive signals, including those from the EOM, project to the vestibular nuclei in the toad and, there, are able to influence processing of vestibular afferent signals. We suggest, therefore, that orbital proprioceptive signals may play a part in oculomotor control. The significance of the results is discussed in relation to the strategic position of the VN in the oculomotor control system.

Acoustic Stimulation↗
PubMed1984

Directional selectivity in the responses of units in cat primary visual cortex to passive eye movement.

The responses of single units in the primary visual cortex (Area 17) of anaesthetized, paralysed cats, to passive movement of the ipsilateral eye were studied. Responses to passive eye movement were found in about one-third of the cortical units isolated. Appropriate control experiments excluded visual, auditory and cutaneous inputs as the source of the effective signal during passive eye movement. The magnitudes of the responses to a number (usually four) of radial directions of passive eye movement were estimated from sets of peristimulus time histograms "interleaved" in time. Units were defined as "radially selective" if the responses to movement along one radius (e.g. vertically upwards) exceeded that along at least one other orthogonal radius (e.g. horizontal-temporal). Of 60 units tested, 53 (88%) were "radially selective" according to this definition. Some of the "radially selective" units showed an additional type of specificity to passive eye movement: (a) Some units responded preferentially to movement along one of the arcs of passive eye movement which were tested (e.g. vertical movement above the equator of the orbit). These units we have called "arc selective". (b) Other units were sensitive to the direction of movement and preferred movement in a particular direction over more than one arc (e.g. horizontal movement towards the temporal side in both nasal and temporal halves of the orbit). These we have called "direction selective". Twenty-one "radially selective" units showed one of these additional properties, nine were arc selective and twelve were direction selective. The implications of these results for the understanding of the function of orbital proprioceptive signals in the cortex are discussed briefly. Responses to passive eye movement were found in all of layers II-VI in Area 17 and the implications of this for the understanding of the pathway by which orbital proprioceptive signals reach the primary visual cortex are discussed. The experiments have shown that many units in cat visual cortex respond to passive eye movement and that most of these units have some specificity for particular radial directions of movement while some have additional specific properties. We believe that these properties of radial, directional and arc sensitivity are likely to be important in understanding the function of the orbital proprioceptive signal which arises during eye movement and they are particularly interesting in relation to the findings of others that this proprioceptive signal appears to be concerned in the normal development of visual properties in the cortex and in the control of visually guided movement in adult cats.

Animals↗