Ht. Schupp et al., POSITIVE SHIFTS OF EVENT-RELATED POTENTIALS - A STATE OF CORTICAL DISFACILITATION AS REFLECTED BY THE STARTLE REFLEX PROBE, Electroencephalography and clinical neurophysiology, 90(2), 1994, pp. 135-144
Cortical positivity as measured by slow event-related potentials is as
sumed to represent a decreased excitability of cortical networks and s
uppression of their behavioral-cognitive output. The blink reflex prob
e is a commonly used defensive electromyographic response whose amplit
ude was shown to be modulated by emotional and attentional orientation
. It was used here as an indicator of cortico-subcortical excitation.
In study 1, 33 healthy subjects took part in a continuous performance
test (CPT). Event-related potentials were recorded from 15 standard sc
alp locations. Acoustic startling noise bursts were delivered during c
onditions that required either performance of prepared motor responses
(Go), inhibition of prepared motor responses (NoGo), or had no motor
significance (Irrelevant condition). During the NoGo condition, EEG su
rface potentials showed a widespread P300-like positivity with a centr
al maximum. Startle responses were inhibited during the NoGo condition
as compared to the Irrelevant condition. In study 2 (21 subjects) the
same format was used, except that the startle reflex was elicited vis
ually. Startle reflexes again showed smaller magnitude during the NoGo
condition, which evoked larger positivity at central sites in compari
son to the Irrelevant condition. The relationship between positivity i
n the EEG and inhibited startle responses is in line with the hypothes
is that positive EEG shifts reflect a state of cortical disfacilitatio
n.