Prefrontal activation evoked by infrequent target and novel stimuli in a visual target detection task: an event-related functional magnetic resonance imaging study.

An event-related functional magnetic resonance imaging study of prefrontal cortex was conducted during which subjects performed a visual "oddball" target detection task. Exemplars of three stimulus categories were presented at a rate of one per 1.5 sec for 10 runs, each consisting of 132 trials. Standards were color squares of varying sizes that were presented on approximately 92% of trials. Targets were color circles of varying sizes presented irregularly on approximately 4% of trials. Novels were pictures of everyday objects that were also presented irregularly on approximately 4% of trials. Ten subjects participated in two separate sessions in which they were required to count mentally or to push a button whenever a target appeared. Targets evoked activation within prefrontal cortex, primarily within the middle frontal gyri (MFG). This MFG activation did not differ as a function of the required response. Novels did not evoke significant activity within this region despite evidence from a separate behavioral and event-related potential study demonstrating their strong influence on processing. In additional imaging sessions with two subjects, the rules were reversed to require a button press whenever an object, but not a circle, appeared. These former novels now evoked activation in the MFG, but the former target circles did not. These experiments indicate that MFG activation is reliably evoked by exemplars from arbitrary stimulus categories that are mapped by experimental rules onto an arbitrary covert or overt response.

The relationship of mismatch negativity to quantitative EEG and morphological findings in schizophrenia.

The goal of the present study is to investigate the relationships of mismatch negativity (MMN) to other markers in schizophrenics; Quantitative EEG (QEEG), CT and psychopathological ratings. Thirty unmedicated patients (28.4+/-9.8 y, 20 M) including twenty neuroleptic-naive cases were divided into two groups before treatment; Group A consisted of ten patients with greater MMN amplitudes, while twenty patients with smaller ones were assigned to Group B. In QEEG, Group A showed a closer profile to healthy controls, indicating their function is less distorted. Group B showed greater power in slow wave, slow alpha and fast beta bands. Their greater slow wave may be implicated in cognitive impairment reflected by attenuated MMN as well as greater dilation in lateral ventricles and Sylvian fissures on CT. After pharmacological treatment with conventional neuroleptics, Group A's MMN decreased, whereas that of Group B increased. Furthermore, neuroleptics' EEG-effects observed in Group A were close to the reported profiles of healthy subjects, while those in Group B were distinct from them. Conclusively, MMN might have crucial associations to other measures underlying the brain pathology of schizophrenia. The diagnostic value of MMN as a trait-marker was discussed.

It takes longer to recognize the eyes than the whole face in humans.

Brain responses to eyes and whole face were studied by magnetoencephalography (MEG). We used five different visual stimuli, face with opened eyes, face with closed eyes, eyes, scrambled face, and hand. 1M was evoked in response to all kinds of stimuli but 2M peaking at approximately 180 ms was recorded only for face and eyes. The peak latencies of 1M and 2M and the interpeak latency 1M-2M to eyes were significantly longer than those to face, and there was no significant difference of latency between face with opened eyes and face with closed eyes. The 2M both for face and eyes was generated in the same area, the inferior temporal cortex, around the fusiform gyrus.

Human face perception traced by magneto- and electro-encephalography.

The temporal and spatial processing of face perception in normal subjects was traced by magnetoencephalography (MEG) and electroencephalography (EEG). We used 5 different visual stimuli: (1) face with opened eyes, (2) face with closed eyes, (3) eyes, (4) scrambled face, and (5) hand, and they were shown in random order. Subjects were asked to count the number of hand stimuli. To analyze the complicated brain responses to visual stimuli, we used brain electric source analysis (BESA) as the spatio-temporal multiple source model. In MEG recording, the 1M and 2M components were identified in all subjects. The 1M component was recorded to all kinds of stimuli. The 2M component was clearly identified only to face stimulation in all subjects, but to eyes stimulation in only 3 subjects with a small amplitude. The 2M component was not identified to scrambled face nor hand stimulation. The 2M component was recorded from the right hemisphere in all subjects, but in only 5 of 10 subjects from the left hemisphere. The mean peak latencies of the 1M and 2M components were approximately 132 and 179 ms, respectively. The interpeak latency between 1M and 2M was approximately 47 ms on average but the interindividual difference was large. There was no significant difference of the 2M latency between face with opened eyes and face with closed eyes. The 1M component was generated in the primary visual cortex in the bilateral hemispheres, and the 2M component was generated in the inferior temporal cortex, around the fusiform gyrus. In the EEG recording, face-specific components, positive at the vertex, P200 (Cz), and the negative at the temporal areas, N190 (T5') and N190 (T6'), were clearly recorded. The EEG results were fundamentally compatible with the MEG results. The amplitude of the component recorded from the right hemisphere was significantly larger than that from the left hemisphere. These findings suggest that the fusiform gyrus is considered to play an important role in face perception in humans, and that the right hemisphere is more dominant. Face perception takes place approximately 47 ms after the primary response to visual stimulation in the primary visual cortex, but the period of information transfer to the fusiform gyrus is variable among subjects. Detailed temporal and spatial analyses of the processing of face perception can be achieved with MEG.

Relationship of mismatch negativity to background EEG and morphological findings in schizophrenia.

The present study assessed relationships of mismatch negativity (MMN) of schizophrenics with other markers; quantitative EEG (QEEG), computed tomography (CT) and psychopathological ratings. Patients were divided into two groups before treatment; group A consisted of patients with greater MMN amplitudes while patients with lower ones were assigned to group B. In QEEG, group A showed no significant differences compared to controls, except for fast beta in the frontal region. The finding of well-preserved QEEG in group A indicates their function is less distorted than in group B, who showed greater powers in slow waves, slow alpha and fast beta bands. The greater slow-wave power of group B may be related to the cognitive impairment reflected by attenuated MMN, which corresponded to greater dilation in lateral ventricles and Sylvian fissures of group B on CT. Conclusively, MMN have crucial relationships to other biological markers representing the psychopathology of schizophrenia.

[ERP study of information processing disturbance on schizophrenia--from aspects of automatic processing and controlled processing].

We studied the relationship between automatic processing and controlled processing in schizophrenic disorder and examined the changes of the relationship through various clinical courses of the illness using event related potentials (ERPs). Thirty schizophrenic patients were classified into two groups according to ERP variations; group-A consisted of schizophrenics who showed higher mismatch negativity (MMN) amplitudes and lower P300 amplitudes than group-B patients. After pharmacological treatment, MMN amplitudes decreased and P300 increased in group-A patients. On the other hand, MMN amplitudes increased, but no significant changes in P300 amplitudes were recognized in group-B patients. MMN amplitudes had a negative correlation with the extent of dilatation of the left Sylvian fissure and the bilateral lateral ventricles on CT scans. From these results, it is suggested that automatic processing and controlled processing complement each other in information processing of schizophrenics. In group-A, higher MMN amplitudes suggested plasticity of processing dysfunction, which showed good social adjustment after pharmacological treatment. In group-B, more severe vulnerability to the disorder was suggested from lower MMN amplitudes, which showed poor social adjustment after the treatment.