The Eletrophysiology of Prepulse Inhibition

The acoustic startle response is decreased by a prepulse occurring
30-500 ms earlier. This prepulse inhibition (PPI)
is interpreted in terms of the Interruption and Protection
hypotheses, in which startle responding interrupts prepulse
processing, and PPI indicates the degree to which prepulse
processing is protected from that interruption. We
evaluated this hypotheses by measuring startle responding
and evoked potentials (N1, P2) to both prepulse and startle
stimuli under different attentional conditions (Attend
Startle, Attend Prepulse, Ignore Both). 192 trials were presented
in randomized order: Startle Alone (105dB noise),
Prepulse Alone (70dB noise), and prepulse+startle stimuli
with a stimulus onset asynchrony (SOA) of 120 (PPI120)
or 500 ms (PPI500). 36 participants, randomly assigned to
the three attention conditions, pressed a key to the startle
or to the pre-pulse or did not respond. A 32-channel
EEG and eyeblink EMG were measured. Independent of
the attentional conditions, the EMG startle response was
decreased by a pre-pulse at both SOAs, illustrating PPI.
Prepulse N1/P2 amplitude was identical for the Prepulse
Alone, PPI120, and PPI500 stimuli independent of the attentional
conditions, demonstrating protection of primary
sensory prepulse processing. N1/P2 potentials to the startle
stimulus were affected by the SOAs and the attentional
conditions, suggesting a change in startle processing by
both variables. The results suggest a complete protection
of prepulse processing. The reduced N1/P2 amplitudes to
the startle stimulus at both SOAs suggest that the eliciting
properties of the startle stimulus are decreased by the prepulse.