Showing papers by "Martha E. Shenton published in 1997"

ERP assessment of visual and auditory language processing in schizophrenia.

Abstract: Language disturbance in schizophrenia has been recently attributed to disturbed priming mechanisms. In the present study, event-related potentials (ERPs), were recorded to final words in sentences presented to 13 chronic patients with schizophrenia and 12 normal controls. Half of the final words fit a sentence context and another half did not. The N400 (the ERP sensitive to language) latency was prolonged, and its amplitude was more negative to both correct and incorrect sentence endings in the group with schizophrenia relative to the group of normal controls. The early ERP components, N100 and P200, were similar in both groups. These results suggest that language abnormalities in schizophrenia are related to a dysfunction in the language system and not to a general cognitive dysfunction, and may be related to poor use of context in patients with schizophrenia.

Aberrant Semantic Activation in Schizophrenia: A Neurophysiological Study

Abstract: Objective: Schizophrenia has long been thought to be characterized by a fundamental disturbance in semantic associations, which has often been presumed to be of neurobiological origin. The authors examined the neurophysiological characteristics of semantic processing in schizophrenic patients. Method: During EEG recording, 15 schizophrenic patients and 15 age-matched comparison subjects read sentences that had either sensible or nonsensical endings. The authors recorded the N400 component, a specific negative event-related brain potential occurring approximately 400 msec after the final word in the sentence. N400 is highly, if not uniquely, sensitive to semantic expectancy and context, and larger, more negative N400 amplitude is associated with increased semantic unexpectancy. Results: In relation to the normal comparison subjects, the schizophrenic patients demonstrated prolonged N400 latency after nonsensical sentence endings and also showed enhanced N400 negativity, regardless of the sense of the sentence ending. Conclusions: These findings suggest slower and more diffuse semantic activation in patients with schizophrenia, perhaps reflective of a disease-related failure to maintain and to use semantic context. (Am J Psychiatry 1997; 154:640‐646)

Parcellation of the human prefrontal cortex using MRI

Abstract: A methodology was developed for dividing prefrontal cortical gray matter into insular, orbital, inferior, middle, superior, cingulate, and frontal pole regions using anatomical criteria. This methodology was developed as a follow-up to one that measured whole prefrontal gray and white matter volumes in schizophrenic and control subjects. This study showed no overall volume differences in prefrontal cortex between schizophrenic and control subjects. The parcellation of prefrontal cortex was done to increase the probability of detecting abnormalities that were circumscribed to a particular portion of the region. A 1.5 Tesla magnet was used to acquire contiguous 1.5-mm coronal slices of the entire brain. Volumes were then measured in a group of right-handed male (n = 15) subjects. Gray matter was parcellated using criteria that were mainly based on gross anatomy, as visualized in 3-dimensional renderings of the brain. Reliability of the parcellation scheme was very high (r(i) = 0.80 and above). This methodology should be useful in the study of cortical pathology in a number of neurological disorders, including schizophrenia.

Update on Electrophysiology in Schizophrenia

Abstract: Event-related potentials (ERPs) provide a non-invasive, functional method to evaluate neural activation and cognitive processes in schizophrenia, with a temporal resolution in the millisecond range, literally at the speed of thought. Auditory ERP components tested in schizophrenia, in order of latency of occurrence, include the P50 sensory gating response, the mismatch negativity, P300, and the N400 component. Abnormalities in these components demonstrate pervasive disruption of auditory processing as early as 50 milliseconds after stimulus onset. All of these abnormalities appear to tasks which require sensory memory or working memory operations. The anatomic substrates for these ERP components probably include the posterior superior temporal gyrus and medial temporal lobe structures. P300 topographic asymmetries have been associated with left posterior superior temporal gyrus abnormalities. Future work will focus on relating ERP abnormalities to specific neural circuit disturbances in this disorder.

Experimentation with a transcranial magnetic simulation system for functional brain mapping

Abstract: We describe functional brain mapping experiments using a transcranial magnetic stimulation (TMS) device. This device, when placed on a subject's scalp, stimulates the underlying neurons by generating focused magnetic field pulses. A brain mapping is then generated by measuring responses of different motor and sensory functions to this stimulation. The key process in generating this mapping is the association of the 3D positions and orientations of the TMS probe on the scalp to a 3D brain reconstruction such as is feasible with a magnetic resonance image (MRI). We have developed a system which not only generates functional brain maps using such a device, but also provides real-time feedback to guide the technician in placing the probe at appropriate points on the head for achieving the desired map resolution. Functional areas we have mapped are the motor and visual cortex. Validation experiments to date have consisted of repeatability and symmetry tests for mapping the same subjects several times. Applications of the technique include neuranatomy research, surgical planning and guidance, treatment and disease monitoring, and therapeutic procedures.