Biomedical subjects

H Bahramali

Publications and source records attributed to H Bahramali.

11 recordsLinked to original sources

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↗

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

Different psychopathological models and quantified EEG in schizophrenia.

BACKGROUND: This study compared the ability of two different models of psychopathology in schizophrenia to account for findings in the quantified electroencephalogram (qEEG) recorded from midline sites in a group of 40 subjects with schizophrenia. The first model was based on the positive and negative syndrome dichotomy, the second was a tripartite model that resembled Liddle's syndromes of psychomotor poverty, disorganization and reality distortion (Liddle, 1987a). METHODS: A group of 40 subjects with predominantly chronic schizophrenia was assessed with the Positive and Negative Syndrome Scale (PANSS) prior to the acquisition of their quantified electroencephalogram. The relationship between EEG data and symptomatology was explored, initially with the PANSS positive and negative subscales and then with a tripartite model derived From a principal component analysis of the 14 positive and negative subscale items. RESULTS: The tripartite syndrome model showed a greater concordance with the qEEG of the subjects than the dichotomous model. 'Psychomotor poverty' was significantly positively correlated with both delta and beta power and 'reality distortion' was significantly positively correlated with alpha-2 power. No significant correlations between the positive and negative syndrome dichotomy and the qEEG were observed. CONCLUSIONS: This study lends support to the factor analysis of psychopathology, and specifically the tripartite syndrome model of schizophrenia, as a step in explicating the biological dimensions of the disorder.

Adolescent↗

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↗

PubMed1999

Is the target-to-target interval a critical determinant of P3 amplitude?

The P3 amplitude is augmented by decrements in target-probability, increments in the number of nontargets preceding the target, and extensions of the interstimulus interval (ISI). Each of these changes prolongs the target-to-target interval (TTI) and, consequently, results attributed to these factors might, at least partially, be accounted for by the TTI. Recent research also indicates that the P3s elicited by targets in one-, two-, and three-stimuli tasks (in which the TTI remains invariant) are similar. However, the TTI has not been examined systematically in previous research. The present study had subjects listen to a randomized ISI (0.5, 1, 2, or 4 s) version of the auditory oddball task in which targets occurred after one, two, three, four, or five nontargets. Event-related potentials were analyzed based on ISI, sequential structure, and TTI. The study examined sequence and ISI effects independent of TTI effects and demonstrated that extensions of ISI affected N1 but not P3 amplitude, extensions of TTI enhanced P3 amplitude independent of sequential structure, and sequential structure failed to influence P3 amplitude when TTI was controlled.

Adult↗

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↗

PubMed1997

Automatic processing dysfunction in Parkinson's disease.

Simultaneous measures of Event Related Potentials (ERP) and electrodermal activity (EDA) allow the delineation of ERPs that did, and did not, evoke an electrodermal 'Orienting Reflex' (OR). The OR is an automatic reflex invoked by novel or significant stimuli. Our group have developed a model to quantify electrodermal OR activity acquired in conventional late component ERP paradigms with short interstimulus intervals. Target late component (N100, P200, N200, P300) ERPs (acquired in an auditory oddball paradigm) and EDA was examined in 15 Parkinson's disease (PD) subjects and 50 normal controls. Single-trial target ERPs were averaged according to whether or not they elicited an electrodermal OR. Compared with controls, the PD group showed significantly decreased N100 and N200 amplitudes in the OR related ERPs ('Orienting ERPs'). These preliminary findings suggest that conventional late component ERPs can be delineated according to whether or not they evoked an OR. The 'orienting ERPs' in PD showed more significant disturbances compared with controls, than ERPs that did not evoke an OR.

Acoustic Stimulation↗