John J. Straumanis

Combinations of evoked potential amplitude measurements in relation to psychiatric diagnosis

The purposes of this investigation were (1) to determine the extent to which single nonredundant measures, derived from optimal combinations of evoked potential (EP) amplitude measurements, could differentiate between various groups of psychiatric patients and between patients and nonpatients, and (2) to assess the replicability of such discriminations. Somatosensory, visual, and auditory EPs were recorded from 15 locations in 253 unmedicated patients and 99 nonpatients. Multivariate statistical methods were used to reduce the amplitude measurements to sets of factor scores that met specified criteria for entry into discriminant analyses between pairs of the following groups: nonpatients, neuroses, personality disorders, schizophrenias, schizotypal/borderlines, major depressives, and manics. Sensitivity, specificity, and predictive value were assessed for discriminant scores. The discriminant scores yielded many differences between groups, most of which were replicable in split-half analyses. Among these were differences between all six patient groups and nonpatients, and between schizophrenics and nonpsychotics. Split-half discriminant analyses were also performed with 12 measures that were obtained by taking the means of factor scores grouped by sensory modality, time, and spatial location; these variables, used without preselection, provided several replicable diagnostic discriminations.

Attention-Related Effects on Somatosensory Evoked Potentials in College Students at High Risk for Psychopathology

Attention directed to a stimulus elicits a late positive wave in the evoked potential, which has consistently been shown to be of lower than normal amplitude in schizophrenic patients. This study aimed to determine whether a similar deviation from normal occurs in nonpatient college students with extremely high scores on Chapmans Physical Anhedonia (AN) and Perceptual Aberration (PA) Scales. Individuals with such high scores have been shown to deviate from control subjects in ways analogous to schizophrenic patients and are considered to be at high risk for this disorder. Somatosensory evoked potentials (SEPs) were recorded from five scalp locations while subjects counted stimuli to one of four randomly stimulated fingers; SEPs to counted stimuli contained the attention-related late positive wave (P400). The AN (n = 10) and PA (n = 10) groups were compared with normal control subjects (n = 10); in addition, the AN group was compared with schizophrenic subjects (n = 7). P400 amplitudes of ANs were lower than those of normal control subjects matched for age and sex, whereas P400 amplitudes of PAs and their matched control subjects did not differ. P400 amplitudes of ANs did not differ significantly from those of the schizophrenic group, although AN means were somewhat higher. Measurements of SEP peaks preceding P400 yielded few consistent group differences with respect to attention-related changes. The results suggest that ANs, but not PAs, display a pattern of P400 deviation similar to that found in schizophrenic patients.

The attention-related somatosensory evoked potential late positive wave in psychiatric patients

Somatosensory evoked potential (SEP) late waves (P400) associated with selective attention were elicited by having subjects count electrical stimuli to one of four randomly stimulated fingers. P400 amplitude was lower in a diagnostically heterogeneous group of 20 psychiatric patients than in 16 nonpatients. Among patients, a general psychopathology factor derived from the Millon Clinical Multiaxial Inventory was significantly correlated with a factor accounting for most of the P400 amplitude variance. In psychiatric patients, attention-related late activity amplitude is apparently reduced from normal in evoked potentials of all modalities; degree of reduction appears quantitatively related to level of psychopathology.

Effects of lithium and amitriptyline therapy on somatosensory evoked response “excitability” measurements

Somatosensory responses obtained with a variety of stimulating conditions were measured in 14 patients before and during lithium carbonate therapy and in 12 patients treated with amitriptyline. Lithium increased evoked response amplitude, particularly in the early portion, and augmented the dynamic range of test responses following conditioning stimuli of different intensity; excitatory effects were enhanced more than inhibitory. Amitriptyline reduced response amplitude in both early and later portions, but did not affect dynamic range. The effects of amitriptyline were dominant over those of lithium in 3 patients treated with a combination of both drugs.

Psychiatric drugs and the somatosensory P400 wave

The effects of antipsychotic and antidepressant medications on the somatosensory evoked potential (SEP) late wave (P400) were investigated in a diagnostically heterogeneous group of 51 psychiatric patients. SEPs were recorded from five scalp locations while subjects counted electrical stimuli to one of four randomly stimulated fingers. In seven subjects, tested both on and off medication, no significant drug effects were observed. P400 amplitudes of 14 patients being treated with antipsychotic medication were greater than those of unmedicated patients matched for age, sex, and diagnosis. P400 amplitudes did not differ between eight patients being treated with antidepressants and eight unmedicated matched patients. Accuracy in stimulus counting (index of task performance) was significantly correlated with P400 amplitude; more accurate counting was associated with higher P400 amplitude. When 14 medicated and 14 unmedicated subjects, matched for task performance, age, sex, and approximate diagnoses, were compared, P400 amplitude did not differ. These findings suggest that higher P400 amplitudes associated with medication probably reflected improved task performance with medication, rather than a direct action of the drugs on P400. The results suggest the conclusion that lower P400 amplitude in psychosis is not secondary to psychiatric drugs.

EFFECT OF ATTENTION MODIFICATION BY TELEVISION VIEWING ON SOMATOSENSORY EVOKED RESPONSES AND RECOVERY FUNCTIONS

Recovery functions of somatosensory evoked responses have consistently provided measures discriminating between psychiatric patients and nonpatients. The present study was conducted to obtain data bearing on the possibility that patient-nonpatient differences may be attributable to group differences in state of attention. The specific aims were: 1) to determine whether consistent changes in somatosensory responses and their recovery functions accompanied the differences in attentiveness, compared with “resting” conditions, associated with television (TV) watching, and 2) to determine whether alterations in somatosensory evoked response characteristics would be correlated with electroencephalographic (EEG) changes taking place between rest and TV conditions. Somatosensory recovery functions, involving five interstimulus intervals, were measured under rest and TV conditions in 18 subjects. The integrated amplitude of the concurrent EEG was also measured. The results indicated that, although EEG amplitude was significantly reduced during TV viewing, there were no consistent changes in evoked response or recovery function measurements. Also, evoked response variations were not correlated with changes in EEG amplitude. The findings make it less probable that previously found patient-control differences in somatosensory recovery functions resulted from differences in general state of attentiveness. They also indicate that marked intraindividual changes in EEG amplitude may take place without correlated shifts in somatosensory evoked response measurements.

Electrophysiological effects of triiodothyronine and propranolol.

The effects of triiodothyronine (T3), T3 combined with propranolol, and propranolol alone on somatosensory evoked responses (SER) and EEG were studied in 2 groups each of 6 male volunteer subjects. The following results were obtained: (1) T3 increased SER amplitude during the first 100 ms after stimulus. (2) Addition of propranolol elimi nated the SER amplitude increase resulting from T3 administration. (3) Neither T3 nor T3 plus propranolol significantly altered the mean level or the temporal variability of EEG amplitude and frequency. (4) There were no significant effects of propranolol alone on SER and EEG measures.

Spatial Distribution of Sensory Evoked Potentials in Psychiatric Disorders

The topographic dimension has received little attention in evoked potential (EP) investigations of psychiatric patients. Although EPS have been recorded most often from a single lead derivation, some studies involving recordings from more than one site have yielded findings which suggest that the spatial distribution of EPs may be of psychiatric interest. For example, Rodin et al. (1968) in a study of visual evoked potentials (VEPs) observed that assessments of psychopathology in schizophrenics were more often correlated with right than with left hemisphere VEP characteristics. Perris (1974) found that amplitudes of VEPs from the left occiput were lower than those from the right in psychotic depressives while they were ill. Buchsbaum et al. (1977) reported that, in a rapidly cycling manic-depressive patient, a VEP wave was decreased in amplitude at the vertex and increased at the occiput with mania and conversely with depression. Such observations encourage further exploration of EP topography with respect to possible psychiatric correlates.

Psychiatric Diagnosis and EEG-Evoked Response Relationships

This study was conducted to determine whether the patterning of EEG and somatosensory evoked response (SER) variables, as determined by the correlations between them, differs with respect to psychiatric diagnosis. Subjects were 43 nonpatients and 90 psychiatric inpatients. SER modified recovery function recordings provided 36 variables, reflecting amplitude and its variations with different stimulus conditions. A 10-min left parietal EEG was quantitatively analyzed to give mean amplitude and frequency and variability measures. Correlations between EEG and ER variables were compared both for unmatched groups of nonpatients, schizophrenics, psychotic depressions, and nonpsychotics and for smaller age and sex-matched diagnostic groups. The results revealed a number of correlation differences between clinical groups. The nature of the differences suggested diagnostic specificity for EEG-ER patterning, which may provide a new, psychiatrically relevant electrophysiological variable.

Application of Factor Analytic Procedures to Complex Evoked Potential Measurements in Psychiatric Research

Several factor analytic procedures were applied to data gathered with a modified somatosensory evoked potential (SEP) recovery function prodecure in 56 non-patients and 224 psychiatric inpatients. The data were analyzed for each option reflected in three main issues. (1) Which group should be used for calculating the basic factor structure--normals only or all subjects? (2) Should measurements be preadjusted for covariance with variables known to obscure events of interest? (3) Should varimax rotation be used, or are principal components sufficient? Using two criteria, interpretability of factors in relation to experimental design, and their ability to discriminate clinical groups, it appeared that: (1) choice of either population yielded similar results; (2) when measurements were pre-adjusted for covariance more interpretable factors, which also yielded clinical discriminations, were obtained by varimax rotations than by principal components, and (3) when data were not adjusted by covariance, principal component analysis produced a factor which, although less interpretable in relation to experimental design than the varimax factors, provided equivalent clinical discriminations.