Biomedical subjects

C R Lines

Publications and source records attributed to C R Lines.

25 records · Page 2Linked to original sources

PubMed1984

The effect of stimulus intensity on visual evoked potential estimates of interhemispheric transmission time.

Visual evoked potentials (VEPs) to bright or dim lateralised light flashes were recorded from homologous occipital and central sites. In a GO/NOGO reaction time task (Experiment 1) the latency of the N160 component of the VEP was found to be shorter from the contralateral hemisphere by approximately 16 ms at occipital sites, but only 3 ms centrally. In addition, there was a trend for the occipital contralateral latency advantage to increase with decreasing stimulus brightness. In Experiment 2 a wider intensity range and a simple visual reaction time task were employed. Contralateral N160 latency advantages were again found to be larger occipitally (approx 13 ms) than centrally (3 ms). Furthermore the occipital contralateral latency advantage was significantly increased at the lower stimulus intensity, while that from central sites remained constant. These data suggest that two types of interhemispheric relay can be distinguished-a sensory one recorded occipitally and a non-sensory one recorded from central sites.

Corpus Callosum↗

PubMed1984

Visual orientation and detection following lesions of the superior colliculus in rats.

Rats with bilateral lesions of the superior colliculus (SC) or with sham operations were trained on a modified version of the running task of Goodale and Murison (1975). The rats were required to shuttle between two large boxes, one of which required a choice between 5 doors, the other having only 1 door. A flashing distractor light at the side of a box was subsequently presented on once-daily test trials. For half the rats of each group these tests were given at 1 month and for the others at 3 months post-operatively. In agreement with previous studies, the SC-lesioned rats showed an abolition of orienting reactions to the distractor. (This was so in both boxes, i.e. a lower attentional load in the running task failed to alleviate the SC lesion-induced deficit.) However, only in the early-tested rats did the lesion cause a loss of freezing response to the distractor. Since in the late-tested group the rats froze but did not orient, it is suggested that the orienting loss at least in their case cannot be attributed to a partial visual field defect.

Animals↗

PubMed1984

Nasotemporal overlap investigated in a case of agenesis of the corpus callosum.

In primates fibres from nasal retinae project contralaterally and those from temporal retinae ipsilaterally. At the border between these two regions an area of overlap where ipsi- and contralaterally projecting ganglion cells intermingle has been demonstrated in monkeys and cats. However, behavioural studies have failed to provide confirmatory evidence in humans. In this experiment simple reaction times to lateralized light flashes at four points of eccentricity (1/2, 1, 2 and 4 degrees) were recorded in an acallosal female. Responses made by the directly stimulated hemisphere were subtracted from those made by the indirectly stimulated hemisphere to arrive at estimates of interhemispheric transmission time. If present, a region of overlap should result in information being available to both hemispheres and consequently alleviate the need for any interhemispheric crossing. However, a large transmission time was found, even with stimuli presented close to fixation, thereby providing no evidence for the existence of such a region in humans.

Adult↗

PubMed1984

Visual evoked potentials to lateralized visual stimuli and the measurement of interhemispheric transmission time.

Visual evoked potentials (VEPs) to lateralized light flashes were recorded from the parietal midline, and from homologous occipital and central sites, in a GO/ NOGO reaction time task. The N160 component of the VEP was found to be larger over the hemisphere contralateral to the visual field of stimulus exposure at all pairs of lateral electrodes. At the occipital sites only, N160 latency was also shorter from the contralateral hemisphere, by an average of approximately 14 msec. This was not so centrally, where a non-significant value of approximately 4 msec was obtained. These data are considered to be consistent with Milner and Lines' hypothesis that callosal transmission occurs at different rates in different functional regions of the corpus callosum.

Cerebral Cortex↗

PubMed1983

Nasotemporal overlap in the human retina investigated by means of simple reaction time to lateralized light flash.

When light flashes are presented laterally simple vocal and manual responses are faster to stimuli in the visual half-field having direct access to the responding hemisphere (an "uncrossed" reaction) than stimuli which go initially to the nonresponding hemisphere (a "crossed" reaction). In the latter case an interhemispheric crossing is presumably necessary and so the crossed-minus-uncrossed difference (CUD) can be identified with interhemispheric transmission time. This paradigm was used to investigate the problem of whether or not there is an overlap of ipsi- and contralaterally projecting ganglion cells at the border between nasal and temporal areas of the human retina, resulting in dual representation of the midline in the brain. If such an overlap does exist then presenting stimuli on this region ought to result in an abolition of the CUD since information would be equally available to both hemispheres. Accordingly vocal and manual reaction times to flashes presented at 1/2, 1, 2, and 4 deg of visual angle were measured. In both cases a consistent CUD was found and this was present at all four points. These results are interpreted as arguing against the existence of overlap in man though some alternative possibilities are discussed.

Adolescent↗

PubMed1983

Stimulus sampling and the use of distal visual cues in rats with lesions of the superior colliculus.

Rats with bilateral ablation of the superior colliculus (SC) were compared with sham-operated rats in two experiments. In the first, it was found that discrimination performance deteriorated as a function of S-R separation, to a similar extent in both groups. In this experiment, unlike earlier ones which found a deficit, the separation was introduced in a horizontal direction. In the second experiment, spatial orientation in the Morris Swimming Pool was found to be impaired in the SC rats both when the target platform was visible and when invisible. During their presence on the platform, these rats also engaged less often in upward orienting movements, although horizontal movements were of normal frequency. It is proposed (i) that there is an anisotropy in the SC's control of orienting head and eye movements in rats, and (ii) that the swimming pool deficit may be due to an impairment of ambient vision.

Animals↗

PubMed1982

Interhemispheric pathways in simple reaction time to lateralized light flash.

In two experiments, simple reaction time to left-field or right-field stimulation was measured as a function of light intensity. The response made on each trial in Experiment 1 was a finger movement, and in Experiment 2 a spoken word. In Experiment 1, the advantage of "uncrossed" over "crossed" reaction times remained invariant across intensities. In Experiment 2, however, the advantage of right over left visual-field stimuli in eliciting a vocal reaction varied inversely with intensity. It is suggested that the use of vocal reactions may permit an estimation of a visual commissural transmission time.

Adolescent↗