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Biomedical subjects

G McCarthy

Publications and source records attributed to G McCarthy.

At least 145 records · Page 8Linked to original sources
PubMed1988

ERPs predictive of subsequent recall and recognition performance.

By exploiting measures of information processing complementary to those obtained from behavioral studies, electrophysiological studies of human memory may provide insights into the cognitive processes associated with encoding. In the present experiment, subjects viewed words under incidental learning conditions in which each word required a two-choice decision based on semantic criteria (interesting/uninteresting or edible/inedible). Memory for those words was subsequently assessed by a free recall test and then a recognition test. Event-related brain potentials elicited in response to the original presentation of each word were found to differ as a function of later memory performance. Over the 400-800 ms latency range, responses to remembered words were positive relative to responses to forgotten words, especially for recall. These electrophysiological differences are interpreted as reflections of processes that correlated with encoding.

Adult↗
PubMed1988

Comparison of propofol and methohexitone as anaesthetic agents for electroconvulsive therapy.

Propofol was compared to methohexitone for induction of anaesthesia for electroconvulsive therapy. Seizures were significantly shorter after the use of propofol, in respect of both visible seizures and duration of cerebral electrical seizure activity. This suggests the possibility that additional treatments may be needed for the same clinical effect in psychiatric illness when propofol is used as the induction agent. Propofol was more effective than methohexitone at obtunding the hypertensive response to electroconvulsive therapy without causing significant hypotension.

Adult↗
PubMed1988

Localization of human sensorimotor cortex during surgery by cortical surface recording of somatosensory evoked potentials.

The traditional means of localizing sensorimotor cortex during surgery is Penfield's procedure of mapping sensory and motor responses elicited by electrical stimulation of the cortical surface. This procedure can accurately localize sensorimotor cortex but is time-consuming and best carried out in awake, cooperative patients. An alternative localization procedure is presented that involves cortical surface recordings of somatosensory evoked potentials (SEP's), providing accurate and rapid localization in patients under either local or general anesthesia. The morphology and amplitude of median nerve SEP's recorded from the cortical surface varied systematically as a function of spatial location relative to the sensorimotor hand representation area. These results were validated in 18 patients operated on under local anesthesia in whom the sensorimotor cortex was independently localized by electrical stimulation mapping; the two procedures were in agreement in all cases. Similar SEP results were demonstrated in an additional 27 patients operated on under general anesthesia without electrical stimulation mapping. The following three spatial relationships between SEP's and the anatomy of the sensorimotor cortex permit rapid and accurate localization of the sensorimotor hand area: 1) SEP's with approximately mirror-image waveforms are recorded at electrode sites in the hand area on opposite sides of the central sulcus (P20-N30 precentrally and N20-P30 postcentrally); 2) the P25-N35 is recorded from the postcentral gyrus as well as a small region of the precentral gyrus in the immediate vicinity of the central sulcus: this waveform is largest on the postcentral gyrus about 1 cm medial to the focus of the 20- and 30-msec potentials; and 3) regardless of component identification, maximum SEP amplitudes are recorded from the hand representation area on the precentral and postcentral gyri.

Anesthesia, General↗
PubMed1987

High frequency jet ventilation for bilateral bullectomy.

This case report describes the use of high frequency jet ventilation for resection of bilateral lung bullae. Low airway pressures reduced the risk of pulmonary barotrauma. A continuous infusion of ketamine provided acceptable anaesthesia.

Adult↗
PubMed1987

Intracranial recordings of endogenous ERPs in humans.

Target detection and stimulus omission tasks of the type used to elicit scalp P300 and related potentials were studied in a group of 40 patients in whom intracranial electrodes had been implanted during evaluation for epilepsy surgery. Two distinct task-related intracranial ERP patterns have been identified, one in the medial temporal lobe and the other in the frontal lobe. These patterns overlap in time with each other and with scalp P300. The temporal lobe pattern consists of positive potentials dorsal and posterior to the hippocampus, sharp negative potentials within and medial to the hippocampus, and positive potentials in the vicinity of the amygdala. This 3-part pattern has been observed for counted targets in auditory, somatic, and visual modalities and for counted stimulus omissions with latencies that covary with scalp P300. This pattern is absent or greatly attenuated in ignore tasks when targets were not counted. The frontal pattern consists of a widespread negative-positive-negative sequence at deep sites which in some patients inverts in polarity at superficial sites and on the scalp. This pattern is consistent with a source or sources within the frontal lobe. Differences in shape and onset latency between the frontal and medial temporal lobe ERP patterns indicate that the former are not simply a distant recording of the latter. These data strongly suggest multiple contributions to scalp P300.

Acoustic Stimulation↗
PubMed1985

Event-related potentials, lexical decision and semantic priming.

ERPs were recorded during a lexical decision task in order to investigate electrophysiological concomitants of semantic priming. The stimuli were 240 words and 240 nonwords presented one per trial at a fixed intertrial interval. Subjects were required to classify each stimulus as a word or nonword by pressing one of two response buttons. ERPs were recorded from 14 scalp locations, the right suborbital ridge, and the left earlobe, all referred to a balanced non-cephalic reference. RT and error data confirmed that semantic priming occurred under the conditions employed: primed words (those preceded by a semantically related word) were identified as words faster and more accurately than were unprimed words (those preceded by semantically unrelated words or nonwords). ERPs for all stimulus types were characterized by a large positivity peaking between 550 and 650 msec, preceded by a negative-going deflection peaking at approximately 400 msec. ERPs for primed and unprimed words were shown to differ significantly, diverging 200-250 msec following stimulus onset, reaching a maximum near the peak of the negative-going deflection at 400 msec. These differences were observed at locations over both hemispheres and were maximal in the centroparietal region. Although P300 latency differences between primed and unprimed words were also obtained, the priming effect on ERPs at shorter latencies could not be explained solely by P300 latency effects. Possible relationships between these ERP concomitants of semantic priming and P300, N200, and N400 were discussed.

Adolescent↗
PubMed1985

Scalp distributions of event-related potentials: an ambiguity associated with analysis of variance models.

Analysis of variance (ANOVA) interactions involving electrode location are often used to assess the statistical significance of differences between event-related potential (ERP) scalp distributions for different experimental conditions, subject groups, or ERP components. However, there is a fundamental incompatibility between the additive model upon which ANOVAs are based and the multiplicative effect on ERP voltages produced by differences in source strength. Using potential distributions generated by dipole sources in spherical volume conductor models, we demonstrate that highly significant interactions involving electrode location can be obtained between scalp distributions with identical shapes generated by the same source. Therefore, such interactions cannot be used as unambiguous indications of shape differences between distributions and hence of differences in source configuration. This ambiguity can be circumvented by scaling the data to eliminate overall amplitude differences between experimental conditions before an ANOVA is performed. Such analyses retain sensitivity to genuine differences in distributional shape, but do not confuse amplitude and shape differences.

Analysis of Variance↗
PubMed1984

Principal component analysis of event-related potentials: simulation studies demonstrate misallocation of variance across components.

Simulated event-related potential (ERP) components were used to investigate the ability of principal component analysis (PCA), Varimax rotation and univariate analysis of variance (ANOVA) to reconstruct component wave shapes, to allocate variance correctly across components, and to identify the correct locus of simulated experimental treatments. The simulated ERPs consisted of 800 randomly weighted combinations of three 64-point components, corresponding to a 2 X 2 X 10 repeated-measures design with 20 subjects. Covariance PCAs, Varimax rotations and univariate ANOVAs were performed on each of 400 such simulations, 100 with no effect of any experimental treatment and 100 each with main effects on each of the 3 components. Eight hundred additional simulations were performed to investigate the effects of systematic variations in the size of the experimental treatments and the number of subjects per experiment. The wave shapes of the simulated components were reconstructed reasonably well, although not completely, by the rotated principal component (PC) loadings. However, comparison of rotated PC scores with the random weights used to generate the simulated ERPs indicated that PCA incorrectly allocated variance across overlapping components, producing dramatic increases in type I error (the largest in excess of 80%) for ANOVAs on one component when the true treatment effect was on another. Although these results should not be overgeneralized, they clearly demonstrate that the PCA-Varimax-ANOVA strategy can incorrectly distribute variance across components, resulting in serious misinterpretation of treatment effects. Additional simulation studies are needed to determine the generality of the variance misallocation problem; pending the outcome of such studies, results obtained with the PCA-Varimax-ANOVA strategy should be interpreted cautiously.

Analysis of Variance↗
PubMed1982

Is handwriting posture associated with differences in motor control? An analysis of asymmetries in the readiness potential.

Levy and Reid's [1] hypothesis that persons who write using the inverted posture have ipsilateral control of distal limb movements, particularly those involved in handwriting, was tested in three experiments in which asymmetries in the readiness potential (RP) were measured. In the first experiment, each subject executed a self-paced repetitive squeeze. Contralaterally larger RPs were recorded from all subjects, irrespective to handwriting posture. In two other experiments, subjects performed the self-paced squeeze in one condition and wrote a single word repetitively in an analogous condition. Larger RPs were recorded over the contralateral cerebral hemisphere in most inverted-writing subjects in both conditions. Ipsilaterally larger RPs were recorded, however, from some left-handers while writing. These findings suggest that, although control of certain movements may originate from the ipsilateral motor cortex in a small proportion of left-handers, handwriting posture does not index this difference.

Adolescent↗
PubMed1981

A metric for thought: a comparison of P300 latency and reaction time.

We confirm that the latency of the P300 component of the human event-related potential is determined by processes involved in stimulus evaluation and categorization and is relatively independent of response selection and execution. Stimulus discriminability and stimulus-response compatibility were manipulated independently in an "additive-factors" design. Choice reaction time and P300 latency were obtained simultaneously for each trial. Although reaction time was affected by both discriminability and stimulus-response compatibility, P300 latency was affected only by stimulus discriminability.

Brain↗
PubMed1978

Sympathetic blocks.

The results of permanent chemical block of the lumbar symmpathetic chain in patients with inoperable vascular conditions, treated during the three-year period 1973--1975 is presented. The results show that, when unsuitable patients have been rejected by their poor response to continuous local aneasthetic blocks, good results with permanent phenol blocks are attainable. These are mainly in patients whose presenting symptom is pain at rest. The complication-rate was low.

Adult↗