Biomedical subjects

C Rennie

Publications and source records attributed to C Rennie.

27 records · Page 2Linked to original sources

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↗

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

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↗

PubMed1990

Magnetoencephalography and late component ERPs.

The recent emergence of magnetoencephalography is a development that is already yielding results. Its intrinsic sensitivity to the actual source activity, rather than to volume currents, means that its particular value lies in source localization. As well as having proven value in research relating to early evoked response and epilepsy, biomagnetic measurements have been applied to later components. For example, results for the auditory P300 potential indicate the source to lie either in the temporal cortex or the hippocampus. More definite conclusions await further development of the instrumentation. Also, there is much scope for more sophisticated analysis of the magnetic fields, of the electric potentials, or ideally of both together. This is likely to elucidate the largely unknown functional circuitry corresponding to the late components of the response.

Brain Diseases↗

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↗

PubMed1989

The relationship between reaction time and latency of the P300 event-related potential in normal subjects and Alzheimer's disease.

The latency of the P300 event-related potential is though to reflect the time it takes to conclude that a task-relevant stimulus has been presented, i.e. it is an index of cognitive processing time. Reaction time (RT) also reflects cognitive processing time, but additionally reflects the time taken physically to respond to the stimulus. If serial models of information processing are correct, then the P300 latency must be less than RT, and a positive correlation between the 2 measures is to be expected. We examined these hypotheses in 100 normal subjects aged from 18 to 92 years. The P300 component elicited via a 2-tone discrimination task, and RT to the task-relevant tones was measured simultaneously. The resulting correlation between these measures was weak (r = 0.26, p greater than 0.05), and there were instances in which RT preceded the P300 latency. These results are consistent with parallel rather than serial models of information processing. Fifteen patients with Alzheimer's disease were also examined. Three had an abnormally delayed P300 latency, and 7 had abnormally delayed RTs compared with age-matched controls. Simultaneous measurement of the P300 latency and RT may thus help resolve whether dysfunction is evident in neuronal networks concerned with stimulus evaluation or in those concerned with response execution.

Adult↗

PubMed1987

Magnetoencephalography: locating the source of P300 via magnetic field recording.

A description is given of the theory and instrumentation involved in measuring magnetic fields of the brain. The magnetic counterpart of event-related potentials are capable of locating more accurately the generators of these electrical signals. Preliminary results of the first application of magnetoencephalography in Australia are presented. These localize the generator of the auditory P300 event-related potential component to the temporal cortex.

Adult↗

PubMedDate not supplied

The relationship between quantified EEG and skin conductance level.

Electroencephalographic measures (EEG) and skin conductance level (SCL) respectively reflect cerebral cortical activity and sympathetic autonomic activity. Such central and autonomic activities associated with arousal generally have been studied separately, despite their potential to reflect complementary dimensions of reticular-thalamo-hypothalamo-cortical activating networks. In this study, we examined the relationship between cortical (19 EEG sites) and autonomic (SCL) activities recorded simultaneously in 10 normal adults. Two second pre-stimulus EEGs and SCLs were assessed from an habituation paradigm which presented 22 trains of 7 tones in an 'ignore' condition. The mean SCLs of the epochs across subjects showed an initial rise (sensitization) followed by an exponential decline (habituation). Although EEG associated with the tones did not demonstrate such a distinct profile, EEG total power and band powers (beta, alpha and theta) associated with the trains showed a systematic increasing response profile. In the group data the mean SCLs within trains showed a significant correlation with alpha and beta band powers. Finer EEG band analyses indicated that beta 3 at Fz and alpha 2 at Cz showed the strongest separate linear correlations with SCL. beta 3 and alpha 1 at Fz were found to jointly covary with SCL. The findings indicate a substantive relationship between measures of cerebral function and autonomic arousal.

Acoustic Stimulation↗

PubMedDate not supplied

Can wear in total hip arthroplasties be assessed from radiographs?

The validity of wear measurements from total-hip radiographs was assessed using a wear simulator which consisted of a total hip prosthesis mounted on a Plexiglas orientation jig. Wear was mesured by a micrometer device and uni- and duoradiographic methods of wear measurement were used with a variety of acetabular cup orientations. In the initial calibration studies the duoradiographic technique proved to be more accurate. The source of the inaccuracies of the uniradiographic method was determined analytically by means of a geometrical model. Forty-inch or 72'' source-to-object film-distances provided similar accuracy and the errors in wear measurement varied from --0.1 +/- 0.4 mm (2 S.D.) to 0 +/- 0.9 mm for wear magnitudes of 1 and 5 mm respectively, regardless of cup position. In subsequent calibration studies the previous radiographs were compiled to represent seven hypothetical patients at various stages of follow-up whose prostheses exhibited between 1 and 5 mm wear. Clinicians assessed the degree of wear, using both the uni- and duoradiographic techniques, under supervision but unaware of the true position and orientation of the wear track. The resulting errors were of the same order as the wear magnitudes being measured. The location of the measurements on the radiographs was then restricted to approximately the true wear axis but again the errors were so large that it was still impossible to make any valid wear assessments. The calibration runs were therefore terminated at this point and it was concluded that wear measurements could not be made from clinical radiographs.

Arthroplasty↗