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Biomedical subjects

I M Donaldson

Publications and source records attributed to I M Donaldson.

At least 73 records · Page 4Linked to original sources
PubMed1981

Measurement of integrated sensory-motor function following brain damage by a computerized preview tracking task.

A preview tracking task has been developed which has particular application to neurological assessment and rehabilitation. Generated and monitored by a graphic display computer, it permits accurate global quantification of the upper-limb sensory-motor system. The incorporation of 'preview' into the tracking task is considered to significantly increase its effectiveness and relevance in relation to normal daily activities. Applied to three groups of normal subjects, several features of normal psychomotor performance and learning were identified or verified: hand dominance is not significant in overall arm control; learning does not completely plateau; increase in age (15-59 years) results in only a minor overall decrement in performance; an initial wide performance distribution decreases dramatically in subsequent sessions. Applied to brain-damaged patients, particularly head injury or stroke, the preview tracking task allows assessment at regular intervals enabling sensory-motor recovery curves to be generated. The potential of this technique, to help determine the efficacy of therapeutic procedures on the recovery process, is illustrated with the presentation of results from three brain-damaged patients demonstrating zero, significant and disjointed recovery of sensory-motor function. The usefulness of the preview tracking task can be expanded by combination with a less frequently applied but more component specific neurological assessment battery.

Adolescent↗
PubMed1980

Excitation of units in the lateral geniculate and contiguous nuclei of the cat by stretch of extrinsic ocular muscles.

In cats, anaesthetized with chloralose and paralysed, the responses of units in the right lateral thalamus were recorded while the extrinsic ocular muscles (EOM) of the right eye were stretched in the dark. Phasic responses were found in all layers of the dorsal lateral geniculate nucleus (LGNd) and in the perigeniculate nucleus (PGN). A given unit usually responded to stretch of more than one EOM and thus to more than one direction of rotation of the eye in the orbit. LGNd. Of a sample of 76 units in LGNd, 55 (72%) gave visula but no muscle responses and 21 (28%) responded to EOM stretch. In all, 40 units with EOM responses were examined and 25 of the 27 tested (93%) also had visual responses. Of the 40 units, 32 could be allocated to layers, thus; layer A, 8 (25%); layer A1, 20 (63%); layer B, 3 (9%); central interlaminar nucleus, 1 (3%). It is interesting that most of the EOM responses were found in layer A1 which recieves the excitatory visual input from the eye whose EOM were stretched. Muscle responsive units occurred with ON- and OFF-centre visual responses of sustained and transient types. PGN. In PGN, 21 units gave EOM responses and most of them were also excited by visual input. The conclusion is that the LGNd and PGN receive an extraretinal proprioceptive signal which should be present during at least large saccadic eye movements. The anatomical pathways which may be involved and the significance of the signal are discussed briefly.

Animals↗
PubMed1980

Interactions between extraocular proprioceptive and visual signals in the superior colliculus of the cat.

1. The responses of units in the superficial layers of the superior colliculus to stretch of extrinsic ocular muscles (e.o.m.) and to visual stimuli, delivered singly and paired at various inter-stimulus intervals, were studied in chloralose-anaesthetized cats. 2. Most units responded to visual stimuli and about half also gave phasic excitatory responses to stretch of e.o.m. 3. Signals from the e.o.m. of each eye reach both superior colliculi; only those in the colliculus ipsilateral to the e.o.m. stretched were studied in detail. 4. A variety of control experiments provided evidence that the signal leading to the responses to e.o.m. stretch was extraretinal. The strong probability is that the receptors responsible were in the extrinsic ocular muscles or their tendons. 5. Of fifty-six units, twenty-four (43%) showed definite interactions between the effects of visual stimuli delivered to the left eye and those due to stretch of e.o.m. of the right eye whose retina had been destroyed. 6. Interactions were found with both stationary and moving visual stimuli. They involved either enhancement or reduction (sometimes abolition) of the response to either e.o.m. or visual stimulation, particularly the latter. 7. Units with interactions showed one of three types of behaviour. (1) Excitatory responses to visual and e.o.m. stimuli given singly, and interactions when the two types of stimulus were paired at some time intervals. Suppression and abolition of visual responses by preceding e.o.m. stretch was common. (2) Units with little or no excitatory response to e.o.m. stretch applied alone, but with showed reduction of their visual responses by preceding e.o.m. stretch. (3) Units with minimal responses to either type of stimulus presented alone but which gave markedly enhanced responses when visual and e.o.m. stimuli were paired. 8. These interactions between proprioceptive and retinal signals are thought to allow retinal image movements which result from saccades to be distinguished from those due to movement of objects in the external world.

Animals↗
PubMed1979

Coding of visual information by units in the cat cerebellar vermis.

Extracellular records were made of the responses to precisely controlled stationary or moving visual stimuli of 174 units in the cerebellar vermis of cats anaesthetised with chloralose. Identified Purkinje cells and unidentified units responsed similarly. Responses to ON and to OFF steps of a stationary light bar had different characteristics. Some units showed changes in the form of their ON responses related to different positions of the stimulus in their large receptive fields. In some cases changes in response latency from different field positions were also noted. Some units responded only to binocular stimulation and others gave much larger responses to binocular than to monocular stimulation. In addition, some were sensitive to the relative retinal disparity of images and, of these, several were sensitive to vertical as well as to horizontal retinal disparity. Sinusoidally-moving light bars gave responses consisting of one or two bursts of impulses per cycle; the most effective frequency was about 3 Hz. These responses may represent detection of the instant of maximum velocity. The relatively precise coding of retinal disparity in spite of the large size of receptive fields and the coding of position within these large fields is discussed. A possible function for the disparity-sensitive units in the control of vergence is suggested and the relation of this control to visual depth detection and to the estimation of the absolute distance of objects from the animal is discussed.

Animals↗
PubMed1976

The involvement of noradrenaline in motor activity as shown by rotational behaviour after unilateral lesions of the locus coeruleus.

Unilateral electrolytic lesions in the region of the locus coeruleus in rats result in contraversive circling behaviour following the administration of systemic apomorphine or dexamphetamine. In a large group of such animals there was a very good correlation between histological damage to the locus coeruleus and the presence of such rotation. There was a progressive increase in the percentage of rats showing this drug-induced behaviour as ipsilateral cerebral cortical noradrenaline content decreased. Unilateral injections of 6-OHDA produce more selective damage to the noradrenergic locus coeruleus and result in a similar, although less marked, apomorphine- and dexamphetamine-induced rotation. Unlike the rats with electrolytic lesions of the locus coeruleus, those with 6-OHDA injections did not show an increase in ipsilateral striatal dopamine content. It seems likely that the motor asymmetry seen with lesions which involve the locus coeruleus is due to damage to its noradrenergic cells. A possible explanation of the differences between electrolytic and 6-OHDA induced lesion is that the 6-OHDA produces damage to the ventral noradrenergic bundle as well as the locus coeruleus and results in an increase in ipsilateral cerebral cortical 5-hydroxytryptamine.

Animals↗
PubMed1976

Binocular visual mechanisms in cortical areas I and II of the sheep.

1. Units were recorded in the primary and secondary visual areas (V1 and V2) of the sheep. They were stimulated binocularly, using an adjustable prism to vary the disparity. 2. Cells in V1 responded optimally to stimuli with very small or zero disparities, but cells in V2 frequently preferred disparities of several degrees crossed or uncrossed. Many cells in V2 were particularly selective to disparity, often giving no response to a monocular stimulus. 3. Cells preferring the same disparity occur in discrete columns, about 400 muM wide. Changes between columns result from a step displacement of the receptive field of one eye. The disparities encoded in successive columns seem to follow a regular sequence: crossed, zero, uncrossed, zero, etc. 4. In both V1 and V2, cells are clustered, perhaps in columns, according to their orientation preference and ocular dominance. In V2, the constant disparity columns appear to be independent of the orientation clusters.

Animals↗
PubMed1975

Circling behaviour produced by unilateral lesions in the region of the locus coeruleus in rats.

Rats with unilateral lesions in the region of the locus coeruleus circled tightly to the opposite side when given apomorphine or amphetamine. This turning behaviour was transient and disappeared within some 30 days after surgery. It was seen most obviously in animals with severe unilateral destruction of the locus coeruleus, which caused on average a 55% reduction in the level of noradrenaline in the ipsilateral cerebral cortex. It was not marked in animals with partial unilateral lesions of the locus coeruleus, which caused only an average fall in cortical noradrenaline of 22%. It was not seen in sham operated animals or animals in which lesions were placed into adjacent structures such as the cerebellum above, superior cerebellar peduncle laterally, and brain stem ventrally. A clue to the mechanism of this phenomenon may lie in the observation that dopamine in the ipsilateral striatum was increased 5 days after operation, when circling occurred, but had returned to normal by 30 days when circling had ceased. It is suggested that the lesion causes a reduction in impulse traffic in the ipsilateral nigrostriatal pathway, and that circling is due to preferential stimulation of the ipsilateral striatal dopamine receptors by both drugs; apomorphine directly, amphetamine by release of endogenous dopamine.

Amphetamine↗