RESUMEN
Prepulse inhibition (PPI) test has been widely used to evaluate sensorimotor gating. In humans, deficits in this mechanism are measured through the orbicularis muscle response using electromyography (EMG). Although this mechanism can be modulated by several brain structures and is impaired in some pathologies as schizophrenia and bipolar disorder, neural PPI evaluation is rarely performed in humans. Since eye blinks are a consequence of PPI stimulation, they strongly contaminate the electroencephalogram (EEG) signal. This paper describes a method to reduce muscular artifacts and enable neural PPI assessment through EEG in parallel to muscular PPI evaluation using EMG. Both types of signal were simultaneously recorded in 22 healthy subjects. PPI was evaluated by the acoustical startle response with EMG and by the P2-N1 event-related potential (ERP) using EEG in Fz, Cz, and Pz electrodes. In order to remove EEG artifacts, Independent Component Analysis (ICA) was performed using two methods. Firstly, visual inspection discarded components containing artifact characteristics as ocular and tonic muscle artifacts. The second method used visual inspection as gold standard to validate parameters in an automated component selection using the SASICA algorithm. As an outcome, EEG artifacts were effectively removed and equivalent neural PPI evaluation performance was obtained using both methods, with subjects exhibiting consistent neural as well as muscular PPI. This novel method improves PPI test, enabling neural gating mechanisms assessment within the latency of 100-200 ms, which is not evaluated by other sensory gating tests as P50 and mismatch negativity.
RESUMEN
Prepulse inhibition (PPI) consists of a reduction of the acoustic startle reflex (SR) magnitude (measured with EMG) when a startling stimulus is preceded by a non-startling one. This behavior has been extensively investigated in studies related to schizophrenia, since sensory-motor deficit plays a central role in its pathophysiology. However, the same auditory stimuli that trigger the SR also provoke intense auditory evoked responses (AEP), which can be measured with EEG. Comparing these two types of responses, acquired simultaneously, is a great opportunity to investigate the dependence and interdependence of their neural pathways. Nonetheless, so far very few studies have dared to perform such simultaneous recordings, because SR produces strong eye blinks and muscle contraction artifacts that contaminate EEG electrodes placed on the scalp. In this study we investigated the possibility of simultaneously obtaining both the acoustic SR (using EMG) and the AEP (using EEG) measures, through the use of advanced artifact removal techniques, to better characterize PPI in healthy humans.