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Biomedical subjects

R A Meares

Publications and source records attributed to R A Meares.

16 recordsLinked to original sources
PubMed2000

Synchronous cortical gamma-band activity in task-relevant cognition.

Widespread synchronous oscillatory activity, particularly in the gamma ('40 Hz') band, has been postulated to exist in the brain as a mechanism underlying binding. A new method of examining phase synchronicity across multiple electrode sites in specific EEG frequency bands as a function of time was employed, in a conventional cognitive ERP paradigm in 40 normal subjects. A significant late post-stimulus gamma synchronicity response occurred for task-relevant stimuli, whereas for task-irrelevant stimuli no such response was evident. However, an early response was seen for both task-relevant and irrelevant stimuli. This is the first empirical demonstration that widespread synchronous high frequency oscillations occur in humans in relation to cognition.

Acoustic Stimulation↗
PubMed2000

Gamma activity in schizophrenia: evidence of impaired network binding?

OBJECTIVES: Gamma ('40 Hz') rhythms may play a role in the integration of sensory processing activity. Impaired temporal integration may be a key feature of the associated disturbances in schizophrenia. This is the first study to examine the time course of Gamma activity induced in response to stimuli in this disorder. METHODS: Gamma activity induced in response to task-relevant and irrelevant auditory oddball stimuli was examined in 35 medicated schizophrenics and 35 age- and gender-matched normal controls. We employed a moving Welch window with short time FFT to examine the time course of Gamma amplitude. The amplitude spectrum for each time point was de-trended to eliminate any contribution of broad spectrum activity (EEG or EMG) to Gamma amplitude. RESULTS: For targets, schizophrenics showed a significant decrease in post-stimulus Gamma response amplitude in left hemisphere and frontal sites and an increase in right hemisphere and parieto-occipital sites (P<0.0009). The abnormalities correlated with PANSS general symptom scores. In the non-targets (at a different latency), schizophrenics showed a widespread Gamma decrease (P<0.0005). CONCLUSIONS: The Gamma findings in non-targets may reflect an abnormality in appropriately processing irrelevant stimuli. This could result in defective processing of the context (integration) of relevant target information.

Adult↗
PubMed1999

Eye movements reflect impaired face processing in patients with schizophrenia.

BACKGROUND: Impaired processing of faces in patients with schizophrenia may underlie aspects of disturbance in their social interaction. This study examined patterns of eye fixation in subjects with schizophrenia and non-psychiatric controls, while processing a high resolution picture of a neutral face and a nonbiological complex geometric stimulus. METHODS: Ten-second sequences of eye movement were recorded video-oculographically (50 samples/sec) while subjects were "free-viewing" the stimuli. An essential element of the study was customized software that ensured stimulus presentation on a video display only after subjects were fixated upon a centre-screen cue, so that all subjects began stimulus processing from the same point. RESULTS: Compared with the control group, subjects with schizophrenia exhibited reduced scanpath lengths and a tendency toward fewer fixations for the face stimulus. They also showed an initial relative right spatial hemineglect (for the first voluntary fixation) when viewing the Rey figure, but not when viewing the face stimulus. Overall, there were no significant differences between the schizophrenia and control groups in the lateral distribution of subsequent fixations for either stimulus. CONCLUSIONS: Disturbed spatial and temporal patterns of eye movement in some people with schizophrenia may reflect sub-optimal processing of face stimuli, that may predispose these individuals to dysfunctional interpretation of facial communication cues.

Adult↗
PubMed1997

Evoked related potentials associated with and without an orienting reflex.

Late component event related potentials (ERP) and concomitant electrodermal activity (EDA) measures of the orienting reflex (OR) were undertaken in 50 normal subjects. Our group recently developed a model to quantify electrodermal activity in conventional ERP paradigms (auditory oddball) with short interstimulus intervals (ISI). The method was used to classify the presence or absence of skin conductance response following each auditory target stimulus. Using a conventional paradigm in which data is traditionally averaged, single-trial target ERPs were sorted into those with a skin conductance response OR (ERP[+OR]) and those without (ERP[-OR]) an OR, and ERP sub-averages of the two groups were derived. The ERP(+OR) showed significantly larger P300 amplitudes and relatively earlier N200 and P300 latency than those of the ERP(-OR). These findings suggest that using concomitant SCR-ERP measures, separate ERP related processes can be determined, that are complementary to the traditional average measure.

Adolescent↗
PubMed1994

Single photon emission computed tomography (SPECT) measures of brain function in schizophrenia.

This study explores SPECT measured in schizophrenic patients at rest. Left temporal lobe activity was found to be decreased with increasing positive symptoms' scores scores. Medicated patients showed a reversal of this pattern underlying this positive symptom effect. Patients with a recent history of auditory hallucinations showed an atypical right temporal lobe dominance, which occurred independently of medication status. These preliminary data are suggestive of the potential utility of SPECT to elucidate symptom/medication/brain activity interrelationships in schizophrenia.

Antipsychotic Agents↗
PubMed1986

Images of the brain in psychiatry.

In psychiatry, the use of computer-based techniques for constructing images of the brain is relatively recent. Nevertheless, findings that have resulted from their use thus far might provide us with a new perspective in the understanding of mental illness. They raise the possibility that many of the disorders, previously understood primarily in terms of psychosocial factors, are associated with specific abnormalities of brain structure and/or function. Although terms such as NMR, BEAM, RCBF, SPECT and PET are increasingly found in medical and psychiatric journals, few people understand in simple terms the principles on which these techniques are based. In this article the techniques used for constructing images of brain structure and function are explained, and an overview of the findings in psychiatric disorders is presented.

Brain↗
PubMed1979

The menstrual cycle and habituation.

A group of women were studied over two consecutive menstrual cycles, at about one week intervals. Twenty-one of these women had spontaneous ovulatory menstrual cycles, 6 women had anovulatory cycles, and 7 were regular users of oral contraceptives. All cycles were converted to classic 28 day cycles. On each visit, a record was obtained of the subject's galvanic skin responses (GSRs) to 21 successive auditory stimuli. It was found that, during ovulatory cycles, a marked change in the rate of habituation of the GSR occurred around day 14 and day 28. During days 1--14 the mean habituation point (number of GSR responses to sound before 3 successive nonresponses) was 12.4 SE 1.6. This dropped to 6.8 SE 1.6 during days 15--28 (2-tailed t test, p less than 0.001). This change was not found for women on oral contraceptives, who showed consistent habituation rates throughout the cycle (mean habituation point 7.2 SE 1.1). The evidence also suggested that women with anovulatory cycles differed from those with ovulatory cycles in that they did not show a chnage in their habituation point around midcycle.

Acoustic Stimulation↗
PubMed1978

Comparison of spontaneous and contraceptive menstrual cycles on a visual discrimination task.

21 women with spontaneous ovulatory menstrual cycles, and 7 women who were regular users of oral contraceptives were investigated over two consecutive menstrual cycles. There two groups were compared on their two flash threshold performance and on mood ratings. It was found that, for women with ovulatory menstrual cycles, visual sensitivity was enhanced during the late follicular phase of the cycle, as ovulation approached. At other phases of the menstrual cycle (paramenstrual and luteal) visual sensitivity remained constant and comparable to the values found in women who were taking to the values found in women who were taking contraceptives. Women who were taking contraceptives showed no significant variation in visual sensitivity with phase of the menstrual cycle. The overall level of anxiety, as reflected by mood ratings was higher in women with spontaneous cycles compared to those taking contraceptives. Neither group, however, showed significant variation in anxiety with phase of the cycle.

Adolescent↗
PubMed1974

L-dopa and arousal.

In 10 patients with Parkinsonism, treatment with L-dopa was associated with a rise in the skin conductance level and its fluctuations, an increased electromyographic activity in the frontalis muscle, and with faster reaction times. The change of skin conductance in response to a loud noise also increased and its habituation to the repetition of the stimulus was delayed. One patient developed a schizophreniform psychosis and showed high arousal and absent habituation. It is possible that dopamine is the transmitter associated with the arousal reaction and that it plays a part in the pathogenesis of schizophrenia.

Aged↗