Task related difference EEG spectrum--a new diagnostic method for neuropsychiatric disorders

ERDS is a new method that was developed to detect EEG changes during a short mental task (reverse counting). It is recommended for testing cognitive EEG in organic mental disorders. The essence of the task situation is that it needs continuous mental work during a short period of time. The level of task difficulty must be adapted to each patient's actual mental capacity. To preserve continuity of the mental work, the level of difficulty might be changed instantly by the EEG technician in case of a longer break or multiple mistakes by the subject in the task. For analysis, artifact-free EEG sections are manually selected. Differences of pre-task and post-task EEG power spectra (ERDS) and differences of the peak and mean frequencies are calculated. Based on our initial experience on 100 ERDS tests, this method demonstrates cognitive EEG changes related to the task. Each patient's pre-task EEG serves as control data that is compared to post-task changes. Hence, confounding effects on the ERDS test are minimal, i.e., the effect of individual EEG features or those EEG signs of the disease or therapy that are independent of cognitive functions. Therefore, ERDS test results can be considered as markers of cognitive state in diverse pathological conditions. They also enable us to follow changes during the spontaneous course of mental illness or due to therapeutic interventions. Appropriate instruction of patients about the task, attention of the technician in order to preserve the patient's continuous mental work, and to insure patient compliance are very important. Further investigation is necessary for validation of the method and to build a database of tests on healthy population of different age groups and of patients with different psychiatric conditions. Standardization of the test is essential for the introduction of ERDS to the every-day routine of clinical neuropsychiatry.