PubMed Health⌕ Search

Biomedical subjects

R Meares

Publications and source records attributed to R Meares.

At least 19 recordsLinked to original sources
PubMed1995

Numbers of preceding nontargets differentially affect responses to targets in normal volunteers and patients with schizophrenia: a study of event-related potentials.

This event-related potential study systematically varied the number of nontargets (1, 3, 5, 7, 9) preceding the target tone in an oddball experiment and examined the effect of this on N2, P3, and reaction time measures in schizophrenic patients and normal volunteers. Schizophrenic patients were found to have reduced P3 amplitudes, but this reduction was restricted to series when the targets followed an intermediate number (3-7) of nontargets, and not when targets followed a short (1) or long series (9) of nontargets. Although other interpretations of this finding are possible, the pattern of results could be explained by the hypothesis that the refractory period governing the generation of the P3 component was prolonged in schizophrenia.

Adult↗
PubMed1995

Regional differentiation of cortical activity in schizophrenia: a complementary approach to conventional analysis of regional cerebral blood flow.

This study examines an alternative to a narrow locus-of-dysfunction cortical pathophysiology in schizophrenia, which in turn suggests a modified approach to the analysis of data from regional cerebral blood flow studies. The results provide qualified support for a model of impaired differentiation of cortical activity in schizophrenia. As an index of the differentiation of cortical fields, regional gradients of cortical blood flow were examined. Medicated patients (n = 15) failed to show the differentiation of networks in frontal areas during a verbal memory recognition task observed in normal comparison subjects (n = 15). Unmedicated patients (n = 15) at rest tended to lose normal lateralization and had increased gradients in the right frontal area compared with normal comparison subjects.

Adult↗
PubMed1995

Maximum variance of late component event related potentials (190-240 ms) in unmedicated schizophrenic patients.

The averaging of individual late component event related potential (ERP) responses, particularly P300, has revealed significant differences between schizophrenic patients and normal subjects. However, the averaging process removes the variability of the individual epochs that constitute that average. The response-variance-curve (RVC) method quantifies the variability of the individual epochs and allows examinations of windows of maximum variance. In this study, we examine the complementary nature of the RVC method to the traditional averaging approach. The averaged N200 and P300 ERP components differed significantly between the schizophrenic and normal groups, but not between the unmedicated and medicated schizophrenic patients. The RVC measure, on the other hand, revealed systematic differences in variability, maximal between 190 and 240 ms, between the unmedicated and medicated schizophrenic patients. The RVC measure therefore provides a focused time frame in which to examine dysfunctions in information processing and macroscopic scale changes in brain function due to medication.

Acoustic Stimulation↗
PubMed1995

Event related response variability in schizophrenia: effect of intratrial target subsets.

The response-variance-curve (RVC) method quantifies the variability of the individual epochs that constitute the average event related potential (ERP), providing complementary information to that offered by ERPs. Numerous studies have found that average ERP late components of an auditory "oddball" paradigm can differentiate schizophrenic patients from normal subjects. Our previous study of the RVC measure revealed significant differences between medicated and unmedicated schizophrenic patients in the maximum ERP variability from 190 to 240 ms. In the present study of unmedicated schizophrenic patients and normal control subjects, we examined the influence of intertarget intervals (generated by pseudorandom stimulus sequences in an auditory oddball paradigm) on the intratrial effects of ERP variability measured by the RVC. The ERPs of unmedicated schizophrenic patients were characterized by an instability in a latency window corresponding to the N200 component. The effect was particularly large at an intertarget interval of 7.8 s and was significantly reduced on either side of this intertarget interval.

Acoustic Stimulation↗
PubMed1994

The P300 ERP component: an index of cognitive dysfunction in depression?

A number of measures of brain function have suggested that depression is associated with cerebral hypoactivity. This study examines the late components of the event-related potential (ERP), in particular the P300 component, in depression. The P300 component is thought to index the updating of neurocognitive models which are concerned with the prediction of future events. Cognitive theories of depression include the proposition that depression may be characterized by abnormalities in the prediction of future events. The P300 component may therefore provide one neurophysiological index of cognitive dysfunction in depression. Twenty-seven subjects (14 medicated, 13 drug-free) fulfilling DSM-III criteria for Major Depression were compared to 27 age- and sex-matched normal controls. The amplitudes and latencies of N100, P200, N200 and P300 ERP components, reaction time and task accuracy were recorded during a standard auditory discrimination task. No significant differences were found in any ERP component measure or in reaction-time between the groups. Depressed subjects performed the experimental task significantly less accurately than normal controls, but this was not reflected in the ERPs.

Antidepressive Agents, Tricyclic↗
PubMed1994

A drive to play: evolution and psychotherapeutic theory.

Freud's thinking was influenced by evolutionary ideas. He built his theory about the instincts of sexuality and aggression. A third phylogenetically given propensity for behaviour, that of attachment, has been added to traditional theory following the work of Bowlby. We propose that the origins of certain psychiatric disturbances, most notably cluster B personality disorders, are to be found not in those drives which are ancient in evolutionary terms but through a disruption of that which has been most recently evolved, and which involves symbolization. It is manifest developmentally as symbolic play. A case report illustrates the hypothesis.

Adult↗
PubMed1992

An outcome study of psychotherapy for patients with borderline personality disorder.

OBJECTIVE: This study evaluated the effectiveness of well-defined outpatient psychotherapy for patients with borderline personality disorder. METHOD: Thirty patients with borderline personality disorder diagnosed according to the DSM-III criteria were given twice weekly outpatient psychotherapy for 12 months by trainee therapists who were closely supervised. The treatment approach was based on a psychology of self (this term being used in its broad sense), and strong efforts were made to ensure that all therapists adhered to the treatment model. Outcome measures included frequency of use of drugs (both prescribed and illegal), number of visits to medical professionals, number of episodes of violence and self-harm, time away from work, number of hospital admissions, time spent as an inpatient, score on a self-report index of symptoms, and number of DSM-III criteria (weighted for frequency, severity, and duration) fulfilled. RESULTS: The subjects showed statistically significant improvement from the initial assessment to the end of the year of follow-up on every measure. Moreover, 30% of the subjects no longer fulfilled the DSM-III criteria for borderline personality disorder. This improvement had persisted 1 year after the cessation of therapy. CONCLUSIONS: The results suggest that a specific form of psychotherapy is of benefit for patients with borderline personality disorder.

Adult↗
PubMed1991

Measurement of maximum variability within event related potentials in schizophrenia.

One limitation of averaging individual late component event related potential (ERP) responses is that a single average ERP cannot reflect the variability of responses from epoch to epoch. In this article, we describe a method to quantify this variability and determine if any part of the overall ERP reflects a maximum variance through the use of response variance curves. We then apply this method to one disorder, schizophrenia, in which variability of information processing is hypothesized to underlie aspects of the symptomatology. Response variance curves in a group of unmedicated schizophrenic patients reveal systematic differences, maximal between 190 and 250 ms, compared with those in a group of medicated schizophrenic patients and normal control subjects.

Adult↗
PubMed1991

The effects of age on auditory event-related potentials.

The effects of age on event-related potentials (ERPs) elicited during a two-tone discrimination ("oddball") task were examined in 97 normal subjects aged from 17-80 years. Strong relationships were found between age and the latencies of the later ERP components N200 and P300. Furthermore the correlation between age and N200 latency at Pz was marginally higher than that of age and P300 latency. For the entire sample, the increase in P300 latency as a function of age was best described at Cz and Pz by linear regression equations. However, a segmented line model better described the P300/age relationship at Fz--the increase in P300 latency with age in subjects over 61 was five times that of subjects younger than 61 years. In this study the task required button-press identification of the targets--the significance of increased age and a delay in N200 latency is discussed with reference to the possibility of N200 latency indexing the speed of cognitive processing.

Adolescent↗
PubMed1991

Regional cerebral blood flow and recognition memory in elderly normals: potential application to Alzheimer's disease.

Regional cerebral blood flow, a physiological measure of brain function, has been used for the assessment of cognitive dysfunction in Alzheimer's disease. A number of studies have found diminished temporo-parietal regional cerebral blood flow (RCBF) in Alzheimer's disease patients at rest and have differentiated these patients from normal subjects with a high degree of sensitivity. However the majority of the Alzheimer's disease patients have been in the moderate to severe stages of the disorder. Few studies have assessed RCBF in the early stages of Alzheimer's disease. With increasing emphasis now being placed on the early detection of such patients we chose to examine RCBF during a task which made demands on those cognitive processes which are impaired in the early stages of the disease, viz. a recognition--memory task. Using a 32-channel RCBF system, we examined 20 normal control subjects over the age of 60 years and 10 patients with early to moderate Alzheimer's disease. RCBF was examined during a task of recognition--memory, and also at rest. Normal subjects showed a global increase in RCBF, with marked left frontal activation, as compared with when at rest. Resting perfusion was decreased in the Alzheimer's subject, and there appeared to be a greater degree of intersubject variability in flow during activation.

Aged↗
PubMed1990

Normal latency of the P300 event-related potential in mild-to-moderate Alzheimer's disease and depression.

A two-tone-discrimination task was used to elicit the P300 component of event-related (brain) potentials (ERPs) from patients with presumed Alzheimer's dementia of mild or moderate severity, depressed patients of older age, and cognitively normal individuals. Although the average P300 latency of the Alzheimer patients was greater than that of the depressed patients, which in turn was greater than that of older aged normals, none of the group differences in latency were statistically significant. Moreover, when latency was examined on an individual basis, less than one-quarter of the Alzheimer patients had an abnormally delayed P300 for their age. Reaction times and the percentage of correct behavioral responses to the tones did distinguish the Alzheimer from the normal group; on both measures the patients' scores were significantly worse. It was concluded that the performance of a simple tone discrimination task requiring a button-press response does not sufficiently tax those cognitive functions impaired in the earlier stages of Alzheimer's dementia to result in abnormally slowed cognitive processing of the kind reflected in P300 latency.

Aged↗
PubMed1990

Augmentation of auditory evoked potentials in somatization disorder.

Sensory input regulation was examined in terms of augmenting/reducing of auditory evoked potentials in 10 patients with somatization disorder (8 males and 2 females) and 10 age- and sex-matched normal controls. The slope of P1-N1 amplitude change as a function of stimulus intensity was greater in patients compared with controls, suggesting an enhanced central nervous system response to sensory input. Taken together with previous findings of a failure to habituate to incoming stimuli in a similar group of patients, and evidence obtained in somatizers of both over-responding to background stimuli in a simple tone-discrimination task and enhanced parietal activation during selective attention, this finding suggests disturbances in the processes of attention and in the regulation of afferent stimuli in somatization disorder, and may help explain the multiple and chronic complaints characteristic of patients with the disorder.

Acoustic Stimulation↗
PubMed1990

Smooth pursuit eye tracking dysfunction and negative symptoms in schizophrenia.

This study examined the hypothesis that negative symptoms are associated with abnormalities of smooth pursuit in schizophrenic patients. The pursuit eye movements of 25 subjects with schizophrenia and 25 matched normal control subjects were recorded using an infrared eye tracking system and quantified using the log of signal-to-noise ratio (1n S/N). The severity of negative symptoms within the schizophrenic group was rated using the Scale for the Assessment of Negative Symptoms. Previous findings of pursuit abnormalities among schizophrenic patients as a group were replicated. There was, however, no significant association between the eye tracking dysfunction and the severity of negative symptoms.

Adolescent↗
PubMed1989

A modified selective attention auditory event-related potential paradigm suitable for the clinical setting.

Auditory event-related potentials (ERPs) were recorded without practice sessions using a selective attention ERP paradigm modified from Hillyard et al. (1973) in 20 normal individuals who varied across wide ranges of age and educational background. The results concur with previous findings concerning the effects of selective attention on both the earlier and later phases of the ERP waveform. Attended stimuli elicited a larger N1 deflection compared with unattended stimuli. Processing negativity was also elicited by attended stimuli, but not by unattended stimuli. Mismatch negativity (N2) was evident in waveforms to signals as compared with standards, and a late positivity (P3) followed N2 only in waveforms to attended signals. This paradigm may be appropriate for evaluating suspected attentional dysfunctions in clinical populations.

Acoustic Stimulation↗
PubMed1989

Regional cerebral blood flow measurements in the diagnosis of dementia.

The Xenon-133 regional cerebral blood flow technique (rCBF) was used to assess cortical perfusion in a group of 15 elderly patients (mean age = 79.1, SD = 8.7) with a probable diagnosis of Dementia of the Alzheimer type (DAT). Nine had mild DAT and six were in the moderate stages of DAT. These patients were compared with 15 age and sex matched normal elderly controls (mean age = 75.1, SD = 5.6). RCBF was measured in each patient and control at rest with eyes closed. The DAT patients had significantly lower mean global CBF than normal controls (t = -4.63, p less than 0.0001). In addition, a further 15 normal elderly subjects aged 60 to 92 were assessed and combined with the original 15 to allow calculation of a normal range of rCBF for elderly individuals. Seventy-three per cent of the DAT patients fell below the lower limit of the normal range (39.3 - 59.3 ISI units). These results show the possible usefulness of rCBF as an aid in the diagnosis of early DAT.

Aged↗
PubMed1989

The P300 event-related potential and regional cerebral blood flow in patients with Alzheimer's disease.

A number of studies have reported that an abnormal delay in the latency of the P300 event-related potential (ERP) is characteristic of the majority of patients with a dementing process. Another body of research suggests regional cerebral blood flow (rCBF) is significantly reduced in Alzheimer's disease (AD). No previous study has compared the effectiveness of these 2 measures in identifying the same patients with AD. Furthermore, most of the studies on which the above findings are based examined patients in the moderate to severe stages of the disorder. In this study we examined P300 latency and rCBF in 10 patients with mild to moderate Alzheimer's disease, and compared their responses with those of normal subjects of similar age. The P300 component was not evident in 2 of the patients: the remaining 8 had a latency within normal limits for their age. On the other hand, 8 of the patients had abnormally reduced rCBF. These results suggest rCBF measures may be useful for identifying AD in its early stages.

Aged↗