Biomedical subjects

C Rennie

Publications and source records attributed to C Rennie.

At least 19 recordsLinked to original sources

PubMed2001

Arousal dissociates amygdala and hippocampal fear responses: evidence from simultaneous fMRI and skin conductance recording.

The experience and appraisal of threat is essential to human and animal survival. Lesion evidence suggests that the subjective experience of fear relies upon amygdala-medial frontal activity (as well as autonomic arousal), whereas the factual context of threat stimuli depends upon hippocampal-lateral frontal activity. This amygdala-hippocampus dissociation has not previously been demonstrated in vivo. To explore this differentiation, we employed functional magnetic resonance imaging (fMRI) and simultaneous skin conductance response (SCR) measures of phasic arousal, while subjects viewed fearful versus neutral faces. fMRI activity was subaveraged according to whether or not the subject evoked an arousal SCR to each discrete face stimulus. The fMRI-with arousal and fMRI-without arousal data provided a distinct differentiation of amygdala and hippocampal networks. Amygdala-medial frontal activity was observed only with SCRs, whereas hippocampus-lateral frontal activity occurred only in the absence of SCRs. The findings provide direct evidence for a dissociation between human amygdala and hippocampus networks in the visceral experience versus declarative fact processing of fear.

Adult↗

PubMed2001

Substrate utilization during endurance exercise in men and women after endurance training.

We investigated the effect of endurance training on whole body substrate, glucose, and glycerol utilization during 90 min of exercise at 60% peak O2 consumption (VO2(peak)) in males and females. Substrate oxidation was determined before and after 7 wk of endurance training on a cycle ergometer, with posttesting performed at the same absolute (ABS, W) and relative (REL, VO2(peak)) intensities. [6,6-2H]glucose and [1,1,2,3,3-2H]glycerol tracers were used to calculate the respective substrate tracee flux. Endurance training resulted in an increase in VO2(peak) for both males and females of 17 and 22%, respectively (P < 0.001). Females demonstrated a lower respiratory exchange ratio (RER) both pretraining and posttraining compared with males during exercise (P < 0.001). Glucose rate of appearance (R(a)) and rate of disappearance (R(d)) were not different between males and females. Glucose metabolic clearance rate (MCR) was lower at 75 and 90 min of exercise for females compared with males (P < 0.05). Glucose R(a) and R(d) were lower during exercise at both ABS and REL posttraining exercise intensities compared with pretraining (P < 0.001). Females had a higher exercise glycerol R(a) and R(d) compared with males both pre- and posttraining (P < 0.001). Glycerol R(a) was not different at either the ABS or REL posttraining exercise intensities compared with pretraining. We concluded that females oxidize proportionately more lipid and less carbohydrate during exercise compared with males both pre- and posttraining, which was cotemporal with a higher glycerol R(a) in females. Furthermore, endurance training resulted in a decrease in glucose flux at both ABS and REL exercise intensities after endurance exercise training.

Adaptation, Physiological↗

PubMed2001

ERPs associated with and without an "orienting reflex" in patients with schizophrenia.

In this study, we measured traditional late components of the Event Related Potential (ERP: N 100, P 200, N 200 and P 300) in a conventional auditory oddball paradigm, but additionally and simultaneously assessed electrodermal "orienting reflexes (ORs)" in 40 patients with schizophrenia and 40 age and gender matched normal controls. The single epoch ERPs that did and did not evoke an OR, were sub-averaged separately. The control subjects (but not the patient group), revealed delayed P 300 latency in the ERP sub-averages without ORs (ERP-OR), compared with ERP sub-averages with ORs (ERP+OR). Between-group analysis showed reduced N 100, N 200 and P 300 amplitudes (as well as delayed P 300 latency) in the ERP+OR sub-average in patients with schizophrenia. In the ERP-OR sub-average, the patient group also had smaller N 100, N 200 and P 300 amplitudes, but larger P 200 amplitude (compared with normal controls). This study shows the potential to tease out physiologically based OR sub-processes, by simultaneous acquisition and analysis of ERPs and autonomic electrodermal activity. Such ERP sub-averages (based on autonomic responses) highlight that multiple processes overlap across the trial, and their delineation may elucidate more specific patterns of disturbance in schizophrenia, than traditional averaged measures.

Adult↗

PubMed2000

The neural correlates of orienting: an integration of fMRI and skin conductance orienting.

In fMRI studies, the averaging of neural activity across multiple trials might obscure important psychophysiological subprocesses. The orienting response (OR) is a distinctive subprocess signalling the active orientation of attention towards potentially significant events. We sought to elucidate fMRI activity associated with visual stimuli that did or did not evoke simultaneously recorded electrodermal ORs (using customised skin conductance recording). 'With-OR' stimuli were associated with significant activity in the hippocampus, anterior cingulate and ventromedial prefrontal cortex. Averaged analysis revealed activity only in the expected visual circuits. Our results suggest that potentially significant stimuli (with-OR) activate different functional networks to familiar (without-OR) stimuli, and that orienting may therefore be an informative subprocess to consider in cognitive fMRI studies.

Attention↗

PubMed1999

Electrodermal activity in schizophrenia: a quantitative study using a short interstimulus paradigm.

BACKGROUND: Electrodermal activity in response to short interstimulus interval (ISI) stimulation allows aspects of information processing to be examined, but such paradigms cause skin conductance responses (SCRs) to overlap. A signal decomposition method was developed and employed to score the overlapped SCRs. This is the first application of the method to the study of schizophrenia. METHODS: Electrodermal activity of 30 medicated patients with schizophrenia and 50 normal controls was obtained using a conventional auditory oddball paradigm with an ISI of 1.3 sec. Tonic skin conductance level (SCL), phasic SCRs, SCR temporal dynamics, and a range of SCR variables in response to target tones were examined. RESULTS: The schizophrenic group showed reduced response rate, proportion of responders, SCR amplitude, rise time, peak latency, and steady-state response amplitude, over the trial compared with controls. There were no between-group differences in SCL or SCR onset time. CONCLUSIONS: The combined use of a conventional short ISI paradigm and the new SCR scoring method demonstrated new facets of electrodermal hyporeactivity in medicated patients with schizophrenia. The hyporeactivity could not be attributed to changes in tonic arousal or dysfunctions in peripheral sympathetic nerve conductance.

Acoustic Stimulation↗

PubMed1999

Dynamics of SCR, EEG, and ERP activity in an oddball paradigm with short interstimulus intervals.

Studies of concurrent central, and autonomic activity using a conventional event-related potential (ERP) oddball paradigms, are considered useful in elucidating the relationship between central and autonomic responses, but the autonomic response tends to overlap. A new method was used to decompose and score overlapping skin conductance responses (SCR). This method enabled examination of dynamic relationships of phasic SCR, prestimulus electroencephalogram (EEG), and ERP to auditory target stimuli in 50 normal adults. SCR amplitude was negatively correlated to EEG and N200 amplitude. The SCR amplitude changes over time exhibited an exponential decline opposite to those of N200, alpha, and beta. All the fitted exponential functions had a time constant of 1-2 min. The findings suggest that a N200 component, active in the auditory sensory discrimination, is concomitant with the SCR. The narrow range of the time constant may provide a clue to the conjoint processes underlying central and autonomic adaptive functions.

Adult↗

PubMed1998

Decrement of the N1 auditory event-related potential with stimulus repetition: habituation vs. refractoriness.

We examined whether the amplitude decrement traditionally found for the N1 peak of the event-related potential (ERP) with repetition of auditory stimuli results from the process of habituation or from the refractory period of the neural elements underlying the N1 response. These competing accounts of the process underlying the N1 decrement with repetition differ in terms of the predicted effects of variations in stimulus repetition and interstimulus interval (ISI). These predictions were examined using a short-term habituation design with a factorial combination of stimulus repetition and ISI. Forty-five subjects received 21 stimulus trains, each consisting of seven innocuous tones, all at 1 kHz except the sixth, which was a 1.5-kHz tone. Each subject was assigned to one of three ISI conditions (either 1, 3 or 10 s). The results provide little support for the view that N1 response decrement with stimulus repetition reflects a process of habituation. The present results provide greater support for the view that this decrement is based on the separate refractory periods or recovery cycle processes of at least two neural generators contributing to activity in the N1 peak latency range.

Acoustic Stimulation↗

PubMed1998

Dynamic spectral analysis of event-related potentials.

This paper presents a new method for the identification of individual event related potential (ERP) components in both frequency and time domains. Using the similar basis function (SBF) algorithm the method provides a time to frequency transform, representing a frequency domain equivalent of the component waveform. Notable features of the SBF algorithm are that it allows for unevenly spaced sampled functions in both the time and frequency domains, and estimates of spectral densities are obtained by numerical computation of finite Fourier integrals. Application of this method to ERP data from 20 normal subjects demonstrated a similar shape of component amplitude frequency characteristics for traditional late component waveforms (N1, P2, N2 and P3). On this basis, a low-frequency band was found where the component amplitude frequency characteristic was described by a Gaussian function, while the component phase frequency characteristic was a linear function of frequency. These relationships are interpreted as frequency domain equivalents of the component. Transformed to the time domain, they provided an analytical description of the ERP as the sum of positive- and negative-going monopolar waves. The study points to similar mechanisms underlying these component waveforms, and analytically defines dynamic properties for the components both in the frequency and time domains.

Adult↗

PubMed1998

Fast and slow reaction time changes reflected in ERP brain function.

A number of studies have examined the average late component Event Related Potential (ERP) and Reaction Time (RT) in response to multiple target stimuli (across-trial averages). This study demonstrates within-trial differences in ERP brain function associated with relatively fast and slow RTs in 50 normal subjects. A conventional auditory oddball paradigm (with a 1 ISI) was employed. Increased ERP N100 and N200 amplitude (and decreased P200 amplitude), as well as earlier P200, N200 and P300 latency were found in the fast compared with the slow ERP subaverages. These results show the potential to elucidate temporal and spatial dynamics of brain function associated with changes in performance, in conventional "cognitive" paradigms applicable to both health and disease states.

Acoustic Stimulation↗

PubMed1998

Fast and slow reaction times and associated ERPs in patients with schizophrenia and controls.

A number of studies have examined across-trial averaged late component. Event Related Potentials (EPR) and Reaction Times (RT) in response to multiple target stimuli. In this study, within-trial relatively fast and slow sub averages are additionally examined, in 20 patients with schizophrenia and 20 age and sex matched controls. A conventional auditory oddball paradigm. Across-trial ERP average analysis showed smaller N200 amplitude and delayed latency (but larger P200 amplitude) in patients with schizophrenia compared with controls. Within-trial ERP analysis revealed a number of additional findings. Controls showed distinctive differences in fast compared with slow ERP sub averages (smaller P200 amplitude, increased N200/P300 amplitudes and earlier latencies). The schizophrenic group on the other hand, showed relatively similar fast versus slow subaverages (no differences in P200 amplitude and N200 latency). In addition, between-group (within-trial) analyses highlighted significant differences in earlier stages of processing (compared with across-trial averages) in both fast and slow subaverages (increased N100 amplitude in controls). The complementary within-trial (compared with across-trial) data are interpreted with respect to a possible disturbance in inhibitory function in patients with schizophrenia.

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↗

PubMed1997

Decomposing skin conductance into tonic and phasic components.

Overlapping phasic skin conductance responses (SCRs) obtained using short interstimulus interval (ISI) paradigms such as those employed in cognitive research, confound measurement of each discrete phasic SCR as well as the tonic skin conductance level (SCL). We report a method of resolving this problem using a modelling technique that takes advantage of the stereotyped nature of the within-subject SCR waveform. A four-parameter sigmoid-exponential SCR model that describes the entire response, was developed and extended to five-, six- and eight-parameter skin conductance (SC) models. These SC models were successfully curve-fitted to more than 60 SC segments, each containing one SCR or two overlapping SCRs on a sloping baseline obtained from 20 normal subjects. The SC segments were consequently decomposed into their components: the tail of the previous response, one or two SCRs and the SCL. The SCRs free of the complication of overlap were then quantified. The raw SCRs of the same data set were also measured using a standard method. The standard measurement showed a significant reduction of 15% in amplitude and 140 ms in peak latency compared to our method. The basic four SCR model parameters--onset time, rise time, decay time constant and gain--showed increasing inter-subject variability in that order. These SCR model parameters may be studied as variables in normal and patient groups and as indices of treatment response. This quantitative method also provides a means to assess the relationships between central and autonomic psychophysiologic measures.

Adult↗

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

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↗

PubMed1993

Elicitation and habituation of the electrodermal orienting response in a short interstimulus interval paradigm.

The present experiment was carried out to investigate elicitation and habituation of the electrodermal Orienting Response with stimulus trains utilising a short interstimulus interval (ISI) of 1.1 s. We sought evidence for within-train response decrement to repeated stimulus presentation, response recovery to a change stimulus and dishabituation following the change stimulus--the three properties necessary to unequivocally identify a decremental process as habituation. No autonomic study could be found using such a short ISI. Autonomic studies on this time scale are necessary if these measures are to be integrated with central event-related potential (ERP) measures of electrical brain function. Overcoming this paradigm gap required the development of novel measurement procedures to estimate the small electrodermal responses obtained, usually occurring on the recovery slope of the response to the previous stimulus in the train. With our novel measurement procedures, evidence was found indicating that electrodermal activity in such a paradigm exhibited the three classic criteria of habituation.

Acoustic Stimulation↗

PubMed1992

Does the N100 evoked potential really habituate? Evidence from a paradigm appropriate to a clinical setting.

This study examined the N100 component of the event related potential in a habituation paradigm with short interstimulus intervals. The paradigm was designed to be relatively brief in duration (approx. 4 min for each of two conditions), so that it could be used for clinical populations with cognitive dysfunction, in which compliance may be a problem with long paradigms. Two conditions - Ignore and Attend - were employed with normal subjects. In each condition, 15 stimulus trains, each consisting of 10 innocuous tones, were presented. The eighth tone was a change stimulus. There was a fixed interstimulus interval of 1.1 s and an inter-train interval of 5 s. From the perspective of traditional Orienting Response theory, evidence was sought for within-train habituation in terms of diminished N100 amplitude to repeated stimuli, response recovery to the change stimulus, and dishabituation of the response to the following standard stimuli. Habituation was suggested by significant decreases of approx. 50% with stimulus repetition, and response recovery to the change stimulus in both conditions. However, there was no evidence of dishabituation following the change stimulus. These results confirm that N100 fails to meet the formal requirements of response habituation, suggesting instead that it may index an earlier process than the Orienting Response.

Acoustic Stimulation↗

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↗