BRAIN ACTIVITY, SEMANTIC MEMORY, AND WORKING MEMORY IN PSYCHOSIS
Cognitive Neuroscience Laboratory, Department of Psychiatry, McLean Hospital
Dean F. Salisbury, Ph.D, Martha E. Shenton, Ph.D, Robert W. McCarley, M.D
We examine thought processes at the neuronal level through the use of event-related potential (ERP) techniques, which allow for functional imaging of brain physiology at speeds in the millisecond range. Two ERPs, the N400 and the late-positive complex (LPC), are uniquely sensitive to brain operations underlying language processing. In this series of experiments, the processing abnormalities fundamental to thought disorder in schizophrenia are sought, using tests of sentence comprehension and word association. One class of words central to the technique are homographs. These words with multiple meanings present unique opportunities for examining the processes of semantic priming and contextual inhibition in language comprehension. A homograph sentence might read, "The toast was burnt crisp", or "The toast was sincere and heartfelt". The end of the sentence delivers information crucial to selecting the appropriate meaning of the homographic noun. For these sentence tasks, subjects simply determine whether the sentences make sense, with homograph sentences embedded among neutral and nonsense sentences. Similarly, subjects might assess the relatedness of word-pairs or word-triplets under both high- and low-speed presentation rates. This allows for emphasizing the semantic activation component of memory (high speeds) or the working memory component (low speeds). Behaviorally, we can assess whether the type of word (unambiguous noun v. dominant homograph v. subordinate homograph) unduly influences schizophrenic thought, whether abnormalities can be localized to early semantic activation processes or later verbal working memory processes, and whether the ERPs elicited on this task demonstrate a qualitative dissociation in brain function between normal control and schizophrenic subjects.
Key Words. Schizophrenia, Thought disorder, Event-related Potentials, Semantic Memory, Verbal Working Memory
Grant Support. National Institute of Mental Health, RO1 MH58704, Brain activity and language comprehension in psychosis.
Project Sites: Dept. of Psychiatry, Cognitive Neuroscience Laboratory, McLean Hospital.
Project Director: Dean F. Salisbury, Ph.D., Cognitive Neuroscience Laboratory, McLean Hospital, NBG21, 115 Mill Street, Belmont, MA 02178. Email: dean_salisbury@http://hms.harvard.edu
Contact Person: Marie Fairbanks, Administrative Assistant. Tel. No. (617) 855-3786. FAX. (617) 855-3785.
Training Opportunities. No funded positions currently, but trainees are encouraged to call Dr. Salisbury.
Representative Publications.
Salisbury DF, O'Donnell BF, McCarley RW, Nestor PG, Shenton ME. (2000). Event-related potentials elicited during a context-free homograph task in normal versus schizophrenic subjects. Psychophysiology, 37: 456-463.