Prior EEG studies have concentrated on measuring scalp P300 event related potential (ERP) and EEG frequency power in cognitive impairment patients. The P300 component is typically elicited approximately 300 ms after each infrequent target stimulus, with reflecting the context updating and the categorization of relevant tasks [14–16]. Parameters extracted from ERP signals are of clinical interest because they are useful in differentiating the healthy controls from cognitive impairment patients [8, 11, 17]. In the time domain, the majority of studies on P300 in cognitive impairment have reported prolonged latencies and reduced amplitudes in visual or auditory modality [15, 18]. In the frequency domain, the spectral studies on the cognition have reported theta power changes due to increased demands on cognitive processes, such as the presentation of infrequent target stimulus in an oddball paradigm. Therefore, it is possible that the reduction of EEG theta power is a feature of cognitive impairment [2, 15, 19, 20].
