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Biomedical subjects

E W Wright

Publications and source records attributed to E W Wright.

At least 19 recordsLinked to original sources
PubMed1983

Preparation- or intention-to-act, in relation to pre-event potentials recorded at the vertex.

Pre-event potentials were compared in the same subject, for 3 types of forewarned events, in which the foreperiod for orienting or attention began several seconds before the event. All of these trials involved similar non-motor components (expectancy, attentiveness, general orienting to a salient stimulus) but differed in whether motor or non-motor responses were required. A prominent and consistent slow negative shift preceded the pre-set time for a motor response, even when the subject 'vetoed' his intention to act shortly before the pre-set time. Pre-event potentials were absent, or small and brief, when the event was a task-related skin stimulus not involving preparation to move. The findings selectively support the view that mental preparation/intention to act is a necessary and perhaps dominant process associated with the vertex-recorded pre-event, slow negative potential. They also show that such a pre-event potential can appear even when the subject knows he is going to veto his developing intention to act and does not actually move.

Adult↗
PubMed1983

Time of conscious intention to act in relation to onset of cerebral activity (readiness-potential). The unconscious initiation of a freely voluntary act.

The recordable cerebral activity (readiness-potential, RP) that precedes a freely voluntary, fully endogenous motor act was directly compared with the reportable time (W) for appearance of the subjective experience of 'wanting' or intending to act. The onset of cerebral activity clearly preceded by at least several hundred milliseconds the reported time of conscious intention to act. This relationship held even for those series (with 'type II' RPs) in which subjects reported that all of the 40 self-initiated movements in the series appeared 'spontaneously' and capriciously. Data were obtained in at least 6 different experimental sessions with each of 5 subjects. In series with type II RPs, onset of the main negative shift in each RP preceded the corresponding mean W value by an average of about 350 ms, and by a minimum of about 150 ms. In series with type I RPs, in which an experience of preplanning occurred in some of the 40 self-initiated acts, onset of RP preceded W by an average of about 800 ms (or by 500 ms, taking onset of RP at 90 per cent of its area). Reports of W time depended upon the subject's recall of the spatial 'clock-position' of a revolving spot at the time of his initial awareness of wanting or intending to move. Two different modes of recall produced similar values. Subjects distinguished awareness of wanting to move (W) from awareness of actually moving (M). W times were consistently and substantially negative to, in advance of, mean times reported for M and also those for S, the sensation elicited by a task-related skin stimulus delivered at irregular times that were unknown to the subject. It is concluded that cerebral initiation of a spontaneous, freely voluntary act can begin unconsciously, that is, before there is any (at least recallable) subjective awareness that a 'decision' to act has already been initiated cerebrally. This introduces certain constraints on the potentiality for conscious initiation and control of voluntary acts.

Adult↗
PubMed1982

Readiness-potentials preceding unrestricted 'spontaneous' vs. pre-planned voluntary acts.

The nature of readiness-potentials (RPs) that may be associated with fully endogenous, 'freely' voluntary acts was investigated. Restriction on when to act were eliminated and instructions fostered 'spontaneity.' The 'self-initiated' RPs exhibited in these conditions were categorizable into two (possibly three) types, all of which could be exhibited by the same subject. Type I had an early onset at about -1050 +/- 175 msec and a long ramp-like form, resembling self-paced RPs. In type II the main negative shift began at about -575 +/- 150 msec, and at about -240 +/- 50 msec in type III. Type II partially resembled the similarly timed NS' component in self-paced RPs. For acts produced at known, preset times, in which freedom of choice was eliminated but planning to act was required, RPs resembled self-initiated type I RPs and self-paced RPs. All RPs were maximal at the vertex, especially type II even though it was also bilaterally asymmetrical. These distributions suggest that cortical areas other than area 4 and 6 contribute importantly, especially to type II. All RPs, whether in self-initiated or pre-planned acts, appear related specifically to preparation for a motor action. When task-related skin stimuli replaced self-initiated movements, under similar conditions of attentiveness (and expectancy), there were either no or relatively small event-preceding-slow potential shifts. All post-stimulus P300 waves were very large. Two volitional processes are postulated: process I is associated with development of pre-planning or preparation to act in the near future (seconds), whether voluntary choice is present (type I RPs) or absent (pre-set RPs); process II, with an onset at roughly 0.5 sec before the act, is associated more uniquely with voluntary choice and with the more specific as well as endogenous urge or intention to act; it can be present in the comparative absence of or in sequence and overlapping with process I.

Brain↗
PubMed1979

Subjective referral of the timing for a conscious sensory experience: a functional role for the somatosensory specific projection system in man.

Subjective experience of a peripherally-induced sensation is found to appear without the substantial delay found for the experience of a cortically-induced sensation. To explain this finding, in relation to the putative delay of up to about 500 ms for achieving the "neuronal adequacy" required to elicit the peripherally-induced experience, a modified hypothesis is proposed: for a peripheral sensory input, (a) the primary evoked response of sensory cortex to the specific projection (lemniscal) input is associated with a process that can serve as a 'time-marker'; and (b), after delayed neuronal adequacy is achieved, there is a subjective referral of the sensory experience backwards in time so as to coincide with this initial 'time-marker'. A crucial prediction of the hypothesis was experimentally tested in human subjects using suitably implanted electrodes, and the results provide specific support for the proposal. In this, the test stimuli to medial lemniscus (LM) and to surface of somatosensory cortex (C) were arranged so that a minimum train duration of 200 ms or more was required to produce any conscious sensory experience in each case. Each such cerebral stimulus could be temporally coupled with a peripheral one (usually skin, S) that required relatively negligible stimulus duration to produce a sensation. The sensory experiences induced by LM stimuli were found to be subjectively timed as if there were no delay relative to those for S, that is, as if the subjective experience for LM was referred to the onset rather than to the end of the required stimulus duration of 200 ms or more. On the other hand, sensory experiences induced by the C stimuli, which did not excite specific projection afferents, appeared to be subjectively timed with a substantial delay relative to those for S, that is, as if the time of the subjective experience coincided roughly with the end of the minimum duration required by the C stimuli. The newly proposed functional role for the specific projection system in temporal referral would be additional to its known role in spatial referral and discrimination. A temporal discrepancy between corresponding mental and physical events, i.e., between the timing of a subjective sensory experience and the time at which the state of 'neuronal adequacy' for giving rise to this experience is achieved, would introduce a novel experimentally-based feature into the concept of psychophysiological parallelism in the mind-brain relationship.

Brain Mapping↗
PubMed1977

Suppression of an eplieptiform type of electrocortical activity in the rat by stimulation in the vicinity of locus coeruleus.

Stimulation of the locus coeruleus, or in the vicinity of this nucleus or of its ascending tracts, could markedly suppress the appearance of epileptiform-like ECoG bursts. The latter were induced in rats by a subconvulsive dose of pentylenetetrazol. Electrode sites were identified histologically. A unilateral stimulus suppressed bursts bilaterally. An individual burst already in progress could be aborted, stopping within less than 0.5-1 sec after onset of a stimulus train. The antiepileptiform actions occurred with no evidence of any desynchronizing effect of the stimulus on the resting ECoG; they appear to be different in sites of origin and nature from those reported for stimulation of the reticular activating system. It is proposed that stimulation of the ascending noradrenergic system in the brain stem may limit the development and spread of hyperexcitatory, epileptiform states.

Animals↗
PubMed1967

Responses of human somatosensory cortex to stimuli below threshold for conscious sensation.

Averaged evoked responses of somatosensory cortex, recorded subdurally, appeared with stimuli (skin, ventral posterolateral nucleus, cortex) which were subthreshold for sensation. Such responses were deficient in late components. Subthreshold stimuli could elicit sensation with suitable repetition. The primary evoked response was not sufficient for sensation. These facts bear on the problems of neurophysiological correlates of conscious and unconscious experience, and of "subliminal perception."

Consciousness↗
PubMed1966

An investigation of serum lipoproteins and of their contribution to mild fat in the dairy cow.

1. Tritium-labelled olive-oil triglycerides were introduced into the rumens of lactating cows and the specific activities of the lipids of milk and plasma and of serum lipoproteins were measured. 2. On treatment of serum with dextran sulphate it was found that the lipid of the precipitated beta-lipoproteins consistently had a specific activity-time curve with a maximum comparable in value with, and occurring earlier than, that of the milk fat. 3. On fractionation of the lipids of these lipoproteins it was found that only the triglycerides and diglycerides had specific activity-time curves with maxima greater than that of milk fat, and on radioactivity data alone they are the only blood constituents studied that meet the requirements for being the precursor of milk fat. 4. From a consideration of abundances and the mean specific activities over the period of the experiment it is shown that the contribution of the diglycerides to the radioactivity in the milk fat must have been negligible and that only the triglycerides could have been responsible for all the radioactivity found in it. 5. Although no other fraction could alone have been responsible for all the radioactivity in the milk fat, at least one, the phospholipids, could have made some contribution. 6. It is calculated that 35-48% by weight of milk fat was derived from the beta-lipoprotein triglycerides, according to whether the phospholipids made an improbably large contribution or none at all.

Animals↗