Ray Cooper

Comparison of subcortical, cortical and scalp activity using chronically indwelling electrodes in man

Abstract 1. 1. Intracerebral recordings show that there is little field spread (volume conduction) in brain tissue and that cerebral models with dipoles deep within the brain are not satisfactory. 2. 2. Comparison of subdural and scalp recordings shows that only widely synchronised components of the cortical activity are observed on the scalp. 3. 3. For strictly localised activity the attenuation from cortex to scalp can be as high as 5000 : 1, but for coherent activity over a wide area it may be only 2 : 1. 4. 4. Model experiments indicate that cortical areas of at least 6 sq cm must be involved in synchronous or near synchronous activity before the scalp EEG is observed, using standard working gains. 5. 5. A plea is made for higher working gains for part of routine EEG recordings.

Regional control of cerebral vascular reactivity and oxygen supply in man

Abstract Gold electrodes implanted for treatment of psychiatric disorders and intractable epilepsy were used to measure the local oxygen availability (O2a) in the intact brain. Relative measurement of local blood flow was obtained from micro-thermistors implanted with the electrodes. Recordings were taken during hyperpnoea, hypercapnia, hypoxia and breathing 100% oxygen. Changes of O2a and blood flow were observed during visual and electrical stimulation, changes of posture and heart irregularities. Results are compatible with a regional auto-regulation of local cerebral oxygenation. It is suggested that the Bohr shift of the oxyhaemoglobin dissociation curve by metabolic and arterial CO2 determines the cerebral tissue oxygenation during short-lived changes of metabolic rate and respiratory variations.

Inhibition of cortical evoked potentials and sensation by self-initiated movement in man

AN imposed, passive or externally paced displacement (EPD) of the index finger in man evokes brain potentials that differ in delay and waveform for postcentral, precentral and prefrental areas1. Displacement so imposed leads to less accurate subjective estimation of limb position from that obtained by self initiated movement2. This behavioural observation as far as we know has not been neurophysiologically investigated with cortical recordings from the human brain. Thus we compared the cortical potentials following passive or externally paced displacement, to those related with a similar but self paced voluntary displacement (SPD) of the left index finger. Not only is self-initiated movement manipulative, however, it also subserves acquisition of sensory information. To examine this aspect of finger movement in a second series of experiments we studied the evoked responses and the subjective sensation to brief electrical stimuli applied to the left median nerve at the wrist or the index finger during SPD and compared them with similar responses elicited with the subject at rest.

The contingent negative variation and the excitability of the spinal monosynaptic reflex

A method is described which permits simultaneous measurement of changes in slow electroencephalographic potentials (Contingent Negative Variation—CNV) and the excitability of the spinal monosynaptic arc (H reflex) during the foreperiod of a simple reaction time experiment. Data from 11 normal subjects show that during the development of the CNV there is an augmentation of the amplitude of the H-reflex. It is suggested that the two phenomena are controlled by a common subcortical structure.

Contingent negative variation and evoked responses recorded by radio-telemetry in free-ranging subjects

Abstract 1. 1. Using an 8-channel radio-telemetry system (RTE) records were obtained of the EEG, pulse rate, respiration, evoked responses and Contingent Negative Variation (CNV) in four normal subjects and three patients with intracerebral electrodes. The subjects were free to move about within 30 m of the receiving aerial. Two RTE channels were modified to provide time constants of 7 sec. 2. 2. Auditory stimuli, synchronized with the operation of average response computers, were transmitted to the subjects by a separate radio-control link. These were used as conditional and imperative signals to the subjects to perform various tasks: pressing a button to arrest the imperative signals, turning the pages of a book, inserting pegs in a peg-board and coming to a stop on a bicycle. 3. 3. Responses to the signals were averaged on line with two barrier-grid tubes and a 2-channel Enhancetron and the intrinsic rhythms were analysed with a 2-channel frequency analyser. The pulse rate was indicated by a cardiotachometer. 4. 4. The initil responses and CNV during the reception of paired auditory signals were similar to those seen with direct connection, provided that the subjects were engaged in some task related to the signals. The CNV was attenuated during exercise or conversation only while the subject was inattentive to the signals. 5. 5. The amplitude of the intracerebral responses to the conditional and imperative stimuli in the patients with implanted electrodes was reduced when the scalp CNV was attenuated by isolation or distraction. 6. 6. During the performance of fairly complex tasks following the auditory signals, the CNV terminated only at the completion of the task, not at the moment of muscular effort. 7. 7. The radio-control link was also used to instruct an experimenter when to loss a ball to a subject or to feint. In this situation also the CNV developed only when the subject was sure the ball was in the air and terminated when it was caught. 8. 8. These observations suggest that the interactions of evoked responses and CNV seen in laboratory conditions also accompany normal activity and the performance of everyday tasks.

Emitted cerebral events

Abstract EEG scalp records from human subjects were used to determine if (a) there were emitted cerebral events, similar to evoked potentials which occured when stimuli were expected but absent, and (b) of there were slow waves similar to the contingent negative variation (CNV) which preceded and followed feedback information about response performance. A paradigm was used which included 3 conditions, all of which were modifications of the standard CNNV procedure. The subjects were required to press a button within a time-window which was automatically varied according to their reaction time. In some conditions S2 was omitted randomly and in one condition there was no manual response to the imperative stimulus, but an EEG change which occured within the window was defined as a response. In all conditions subjects were given feedback information about response performance 1.5 sec after the imperative stimulus. The results were analysed using a new pattern recognition technique which did not require averaging of raw data. The results indicated that there were emitted events at the approximate time when the imperative stimulus should have occured on those occasions when it was absent. The emitted events correlated well with potentials evoked by the imperative stimulus when it was present. the results also showed that there were slow waves preceding feedback and following feedback which correlated with the preceeding S1–S2 CNV. These results were discussed in relation to the nature of registration and retrieval mechanisms and also in relation to the findings reported by others of persistent negatively after the CNV in subjects with behaviour pathology.

Event Related Slow Potential Changes in Human Brain Stem

A SLOW negative shift of brain electrical potential can indicate association made between paired stimuli when one acts as a warning and the other an imperative stimulus1. This is termed the contingent negative variation (CNV). Intracerebral recording in man confirmed the cortical origins of the change seen at the scalp. There have, however, been suggestions based on animal studies2–5 that, although essentially a cortical change, the CNV might be mediated by the action of sub-cortical centres, possibly in the thalamus and/or the brain stem and midbrain reticular system. Haider et al. recording from electrodes in thalamus and on the cortex of patients undergoing acute thalamic surgery, have reported characteristic changes in evoked potentials from the ventro-oral nucleus accompanying the appearance of the CNV at the cortex6,7.

Changes of the EEG, intracranial pressure and other variables during sleep in patients with intracranial lesions

Abstract Indwelling pressure transducers, thermistors and gold electrodes have been used to measure intracranial pressure and other variables in neurosurgical patients. During stage II sleep diffuse scalp EEG activity is associated with changes of intracranial pressure and other variables. Possible mechanisms are discussed and it is suggested that, as in animals, cerebral metabolism is increased when the amplitude of the EEG is small (desynchronized) and decreased during periods of large amplitude slow waves.

Effect of the beta adrenergic blocking agent propranolol on essential tremor

A double blind trial of a single 40 mg dose of the beta adrenergic blocking agent propranolol in the treatment of essential tremor produced significant reduction of tremor in four of five patients, but this effect was transient and had considerably diminished within four hours. A months double blind clinical trial of propranolol, in a dose of 30 mg three times a day, showed that the active drug gave statistically better results than placebo for the attenuation of tremor. The mode of action of propranolol in the reduction of essential tremor is probably a dual one, due both to blockage of peripheral beta receptors and to a central depressant effect.

A technique for the measurement of phase relations of the EEG

Abstract A method is described in which the sine and cosine components of the Fourier analyses of multichannel data are displayed as vectors. Common reference recordings are recommended because of the interaction of amplitude and phase differences in bipolar montages.