Osamu Saitoh

Auditory imagery mismatch negativity elicited in musicians

A mismatch between auditory sensation and expectant imagery of syllables elicited a possible equivalent of mismatch negativity in a previous study. The purpose of this study was to verify whether auditory imagery from musical notation could also mediate such imagery-based mismatch negativity. Neuromagnetic recording was obtained from eight musicians, who were instructed to identify unpredictably occurring pitch mismatches between a random tone sequence and a visually presented musical score. The difference between incongruent and congruent responses showed a magnetic distribution consistent with two frontal-negative current dipoles bilaterally located in the vicinity of Heschls gyrus, peaking at approximately 150u2009ms in latency. This imagery-based mismatch negativity may represent an early neural process of deviance detection between the sensory input and expectant imagery.

Correlations of event-related potentials with schizophrenic deficits in information processing and hemispheric dysfunction

In order to obtain further insight into hemispheric dysfunction in schizophrenics, two experiments were conducted employing event-related potential (ERP) recording during dichotic detection tasks as well as syllable discrimination tasks. Results concerning ERPs derived from the T3 and T4 regions are reported. Based on results in the two experiments, it is concluded that schizophrenics display a dysfunction of the left hemisphere, as well as a dysfunction in the ingration mechanism of both hemispheres. It is also speculated that the left-hemisphere dysfunction in schizophrenics is particularly correlated with positive psychotic symptoms.

Verbal memory disturbances in left temporal lobe epileptics

The relationship between laterality of paroxysmal discharges and characteristics of disturbances in memory functioning was investigated in temporal lobe epileptics. Subjects consisted of 22 temporal lobe epileptic patients, in whom the foci of the paroxysmal discharges were localized to one side of the temporal regions. The left focus group consisted of 10 patients; the right focus group, 12. Subjects were required to recognize verbal material presented to one hemisphere by means of a tachistoscope. The left focus group alone failed to demonstrate a right visual field superiority in these tasks. It was concluded that the left focus group specifically demonstrate disturbances in verbal memory functioning, particularly when stimuli were presented to the left hemisphere. Paroxysmal discharges seemed to interfere with normal memory functioning in the region where the foci of these discharges were found.

Behavioral and P3 amplitude enhancement in schizophrenia following feedback training

In order to clarify the remediability of behavioral and electrophysiological abnormalities in schizophrenia, hit rate, reaction time, and P3 amplitude from auditory event-related potentials were evaluated before and after feedback training of a task in 14 schizophrenics and 12 age-matched normal controls. Although mean changes in the three indices due to the training were nonsignificant in both schizophrenic and normal control groups as a whole, the changes in hit rate and reaction time correlated significantly with the P3 amplitude change in the schizophrenic (r = 0.60 and -0.58, respectively) but not in the normal control group. The P3 amplitude change also correlated with the P3 amplitude before the training only in the schizophrenic group (r = -0.68), suggesting that the training was more effective for the schizophrenic patients with marked P3 amplitude reduction. The observed P3 amplitude increase due to training may represent an electrophysiological correlate of a remediable aspect of behavioral deficits in schizophrenics, which may underlie the effectiveness of nonpharmacological treatments.

Distributions of the Nd and P300 in a normal sample

To obtain objective criteria for assessing the attentional and cognitive functioning of psychiatric populations, we attempted to standardize values of two components in Event-Related Potentials (ERPs), namely the attention-related negative potential (Nd) and the P300, in normal populations. The study consisted of 100 healthy volunteers (50 females, 50 males) who were given the task of making dichotic syllable discriminations requiring key-press responses. Their ages ranged between 18 and 59 years (mean +/- S.D., 32.3 +/- 11.3 years). Nd was found to be maximum in the Fz region, P300 being maximum in the Pz region. The means and standard deviations of Nd and P300 areas in their maximum regions were 554.1 +/- 307.8 microV ms and 2148.5 +/- 1248.5 microV ms, respectively. The transformation plot for symmetry indicated the suitable power of transformation to be 1/2 for both Nd and P300 distributions. After being transformed into square-root values, the distribution patterns of Nd and P300 areas were examined. When the lower limit of normal values was tentatively assigned to mean -2 S.D. using square-root transformed data for both Nd and P300, 97% of the subjects were found to display values above the lower normal limit for Nd, and 98% for the P300. Neither, Nd nor P300 areas correlated with age, while P300 latencies displayed a weak positive correlation with age. Females displayed relatively larger values than males for Nd and P300 areas and P300-peak amplitudes. However, the differences between females and males were not statistically significant. Females and males showed nearly equal P300-peak latencies.

Audiovisual phonological mismatch produces early negativity in auditory cortex.

During silent reading, visual information provided by letters is converted to auditory information in the mind. The purpose of this study was to identify the primary locus for auditory verbal imagery in the brain. Neuromagnetic recording was obtained from 10 right-handed study participants, who were instructed to identify infrequently occurring phonological mismatches between a random-ordered sequence of syllable sounds and a visually presented syllabogram sequence. The activity difference in early latency, calculated by subtracting the averaged responses to matched syllables from the averaged responses to mismatched syllables, showed a spatiotemporal profile strikingly similar to that of mismatch negativity. Auditory imagery of forthcoming verbal sounds may establish a memory trace as a template for imagery-based mismatch negativity generation in the auditory cortex.

Reduction of ballistocardiogram with a vacuum head-fixating system during simultaneous fMRI and multi-channel monopolar EEG recording

Abstract Simultaneous EEG/functional magnetic resonance imaging (fMRI) recording seems attractive for neurocognitive in comparison to clinical studies. However, this methodology suffers from a serious artifact called ballistocardiogram. To avoid this artifact, bipolar montage has been used, which is not suitable for numerical analyses. In this study, a vacuum head-fixating system was introduced to realize multi-channel and monopolar EEG recordings. The result was that the ballistocardiogram was almost removed from the artifact contaminated EEG. The recorded EEG did not only enable the monitoring of the subjects status sufficiently, but also obtained a reasonable result from the temporal Fourier analysis.

Psychological Intervention Can Partly Alter P300-Amplitude Abnormalities in Schizophrenics

Abstract: In the present study, we investigated whether psychological interventions can alter P300‐abnormalities, specifically enhancing reduced P300‐amplitudes, in schizophrenics. A three‐tone discrimination task was employed for recording P300s, in which psychological intervention to facilitate target detection was performed through delivering a buzzer sound one second after each designated target tone that informed its occurrence. This procedure was done exclusively during the third and fourth sessions among the six sessions in total. When the data for all the patients were analyzed as a whole, no significant change was observed. However, when the patients were broken down into two groups based on the P300‐amplitudes in the first and second sessions, significant effects of the intervention emerged. The group with smaller P300‐amplitudes showed a significant increase in P300‐amplitudes as well as improved performance levels during and after the intervention sessions. On the contrary, the group with larger P300‐amplitudes displayed a significant decrease in P300‐amplitudes in these sessions. Interestingly, the above results were consistent with the subjective difficulty changes experienced by the patients through the sessions. Overall, the above results indicate that psychological interventions can partly enhance reduced P300‐amplitudes in schizophrenics.

Psychiatric patients showing irregular β activities in EEGs and treatment with antiepileptic drugs : a report of 15 cases

Abstract: Fifteen psychiatric cases are reported who were clinically diagnosed as schizophrenic, affective disorders, or neurotic, but resisted standard medication regimens, all showing irregular β activities on EEGs. The cases tended to display symptoms in common, such as dysphoria, emotional instability or frequent physical complaints. These characteristic symptoms share something mutually with the symptoms shown in some epileptic patients or psychiatric patients with epileptic EEG abnormalities without clinical seizures. Antiepileptic drugs seemed more specifically effective to the above symptoms. More than half of these cases showed improvement on EEG findings such as a decrease in irregular β activities and an increase in rhythmicity or regularity of α activities along with clinical improvement with the administration of adjunctive antiepileptic drugs. These results suggest that the adjunctive administration of antiepileptic drugs to patients with irregular β activities on EEGs is clinically useful and an EEG examination has much value in psychiatric practice to find the criteria of drug therapy.

Event-Related Potentials and Cognitive Deficits in Schizophrenia

Measurements of Event-Related Potentials (ERPs) have been utilized in studies on attentional functioning. Hink, Hillyard and Benson (1978) recorded ERPs during syllable discrimination tasks, and found that the N100 component in normal subjects was enhanced to all stimuli in the attended ear, while the P300 component was enhanced only to the “target” stimuli in that ear. Based on these results, they hypothesized that the N100 component correlated with the ‘stimulus set’, while the P300 component correlated to the ‘ response set’ as defined by Broadbent (1971). Accordingly, ERP measurements are considered to be a useful method for clarifying the pathophysiological bases underlying those diseases that display disturbed attentional functioning. A number of studies measuring ERPs in schizophrenics has already been reported (Levit et al., 1973; Shagass et al., 1978; Roth et al., 1981; Saitoh et al., in press). These reports are nearly consistent in that schizophrenics demonstrate a reduction in P300 amplitudes.