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Biomedical subjects

O Holmes

Publications and source records attributed to O Holmes.

23 records · Page 2Linked to original sources
PubMed1967

Analysis of the activity of one type of spontaneously discharging unit in the cortex cerebri of the anaesthetized rat.

1. Extracellular records from one type of spontaneously active element in the cortex of rats anaesthetized with urethane have been analysed statistically.2. Intensity functions reveal that the frequency of discharge of a unit tends to be modulated periodically, the period being 1(1/2)-2 sec under fairly deep anaesthesia. When anaesthesia becomes lighter, long intervals occur rarely; the unitary discharge becomes less regular and the intensity function becomes flat. Variations in depth of anaesthesia are accompanied by changes in amplitude of the periodic modulation; the period of the modulation is not significantly altered.3. Summed interval histograms indicate that the long intervals are separated by groups of short intervals in a significantly regular fashion. The number of short intervals in a group varies from one to about fifteen, according to the mean frequency of discharge of the unit.4. Serial correlation coefficients reflect the observations of 2 and 3 above but indicate no additional serial correlation. The existence of long intervals obscures any serial patterning of short intervals during bursts.5. Simultaneous records from two units show that the periods of activity in the two units are highly synchronized.6. It is probable that all these features are due to a process which causes periodic synchronous excitability changes of all the spontaneously active elements of the type studied.

Journal Article↗
PubMed1966

Cobalt applied to the sensorimotor area of the cortex cerebri of the rat.

1. In anaesthetized rats, the area of the cerebral cortex where the electrical response to stimulation of the fore or hind paw has a minimum latency was found to bear a fairly constant relation to bony landmarks of the skull. Reasons are given for accepting the site of minimum latency as being the area most closely associated with the periphery.2. In animals under anaesthesia, the cortical areas responding with minimum latency to fore- and hind paw stimulation are spatially distinct.3. Cobalt powder has been applied to one of the two cortical areas where the electrical response to contralateral fore- or hind paw stimulation is a minimum. The animals have been allowed to recover and the time course of the resulting muscular jerks has been followed.4. Jerks occur most frequently and earliest in the contralateral forelimb after the application of cobalt to the forelimb area of the cortex. When the cobalt is placed on the hind limb area, these jerks appear first and occur most frequently in the hind limb. This implies that the cortical areas most closely connected with fore and hind limbs are physiologically distinct in the absence of anaesthesia.5. The limb jerks start to appear after 24 hr, occur with increasing frequency until the 10th day and thereafter decline. The decline in jerking is attributed to the formation around the cobalt of a connective tissue capsule.

Journal Article↗
PubMed1966

Units in the cerebral cortex of the anaesthetized rat and the correlations between their discharges.

1. Extracellular records have been made of spontaneous unitary activity in the cortex of the anaesthetized rat. If the animal is anaesthetized with sufficient urethane almost to abolish reflex contractions of leg muscles when a hind paw is stimulated, two types of spontaneously active unit are found. One type of unit is found in all areas of the cortex which have been studied, and gives high voltage discharges. The other has only been foun in restricted areas of cortex and gives low voltage discharges. 2. The activity of the former type of unit has been analysed. In the unstimulated animal, groups of relatively frequent discharges are separated by periods of quiescence. Apart from this, the discharge pattern appears irregular on naked-eye examination. Synchronous with these periods of frequent discharge, the electrocorticogram exhibits rapid oscillations. Peripheral stimulation of the animal can modify the pattern of discharge of this type of unit. Details of these observations are described. 3. The results are described of experiments in which simultaneous records have been taken from pairs of units in the cerebral cortex. The intensity of correlation between the two units has been measured as a function of temporal displacement (lag) between the two records. 4. With fairly deep urethane anaesthesia, the highest correlation between the two unitary discharges occurs at zero lag if the two units are close together or if they are far apart but in the same coronal line, e.g. if the recording electrodes lie in homologous areas of the two cerebral hemispheres. If one unit is in the anterior pole of a hemisphere and the other in the posterior pole, the discharges are usually synchronous. However, it has sometimes been found that the anterior of the pair of units discharges impulses which precede those of the posterior unit by up to 100 msec. The highest intensity of correlation is then appropriately displaced to 100 msec. 5. The correlation fluctuates rhythmically with a period of 1-8-2 sec, slowly damps out and is symmetrical around the point of highest correlation. 6. Increasing the sensory bombardment of the cortex reduces or abolishes the correlation between the activity of pairs of units. 7. Under Nembutal anaesthesia sufficient to abolish reflex contractions of leg muscles when a hind paw is pinched, no spontaneous cortical unitary activity has been found. When anaesthesia is ligher, spontaneous activity does occur and consists of bursts of up to six impulses at a frequency of 300-500/sec. When simultaneous records from two units have been made, no correlation has been found between their activity.

Anesthetics, Intravenous↗