The effect of prepulse amplitude and timing on the perception of an electrotactile pulse.

The perceived intensity of an intense stimulus as well as the startle reflex it elicits can both be reduced when preceded by a weak stimulus (prepulse). Both phenomena are used to characterise the processes of sensory gating in clinical and non-clinical populations. The latter phenomenon, startle prepulse inhibition (PPI), is conceptualised as a measure of pre-attentive sensorimotor gating due to its observation at short latencies. In contrast, the former, prepulse inhibition of perceived stimulus intensity (PPIPSI), is believed to involve higher-order cognitive processes (e.g., attention), which require longer latencies. Although conceptually distinct, PPIPSI is often studied using parameters that elicit maximal PPI, likely limiting what we can learn about sensory gating's influence on conscious perception. Here, we tested an array of stimulus onset asynchronies (SOAs; 0-602 ms) and prepulse intensities (0-3× perceptual threshold) to determine the time course and sensitivity to the intensity of electrotactile PPIPSI. Participants were required to compare an 'unpleasant but not painful' electric pulse to their left wrist that was presented alone with the same stimulus preceded by an electric prepulse, and report which pulse stimulus felt more intense. Using a 2× perceptual threshold prepulse, PPIPSI emerged as significant at SOAs from 162 to 602 ms. We conclude that evidence of electrotactile PPIPSI at SOAs of 162 ms or longer is consistent with gating of perception requiring higher-level processes, not measured by startle PPI. The possible role of attentional processes, stimuli intensity, modality-specific differences, and methods of investigating PPIPSI further are discussed.

Favero JD ，Luck C ，Lipp OV ，Marinovic W ... -  《-》

N1-P2 event-related potentials and perceived intensity are associated: The effects of a weak pre-stimulus and attentional load on processing of a subsequent intense stimulus.

A weak stimulus presented immediately before a more intense one reduces both the N1-P2 cortical response and the perceived intensity of the intense stimulus. The former effect is referred to as cortical prepulse inhibition (PPI), the latter as prepulse inhibition of perceived stimulus intensity (PPIPSI). Both phenomena are used to study sensory gating in clinical and non-clinical populations, however little is known about their relationship. Here, we investigated 1) the possibility that cortical PPI and PPIPSI are associated, and 2) how they are affected by attentional load. Participants were tasked with comparing the intensity of an electric pulse presented alone versus one preceded 200 ms by a weaker electric prepulse (Experiment 1), or an acoustic pulse presented alone with one preceded 170 ms by a weaker acoustic prepulse (Experiment 2). A counting task (easy vs. hard) manipulating attentional load was included in Experiment 2. In both experiments, we observed a relationship between N1-P2 amplitude and perceived intensity, where greater cortical PPI was associated with a higher probability of perceiving the 'pulse with prepulse' as less intense. Moreover, higher attentional load decreased observations of PPIPSI but had no effect on N1-P2 amplitude. Based on the findings we propose that PPIPSI partially relies on the allocation of attentional resources towards monitoring cortical channels that process stimulus intensity characteristics such as the N1-P2 complex.

Favero JD ，Luck C ，Lipp OV ，Nguyen AT ，Marinovic W ... -  《-》

Effects of prepulse intensity, duration, and bandwidth on perceived intensity of startling acoustic stimuli.

Swerdlow NR ，Blumenthal TD ，Sutherland AN ，Weber E ，Talledo JA ... -  《BIOLOGICAL PSYCHOLOGY》

The medial agranular cortex mediates attentional enhancement of prepulse inhibition of the startle reflex.

The startle reflex, which interferes with on-going cognitive/behavioral activities, is of important protective function for humans and animals. Prepulse inhibition (PPI), as an operational measure of sensorimotor gating, is the suppression of the startle reflex in response to an intense startling stimulus (pulse) when this startling stimulus is shortly preceded by a weaker non-startling stimulus (prepulse). In both humans and laboratory animals, PPI can be enhanced by facilitating selective attention to the prepulse, suggesting that higher-order cognitive/perceptual processes modulate PPI. It has been well known that both the cholinergic system located in the basal forebrain and the deep layers of the superior colliculus in the PPI-mediating circuit are top-down modulated by the medial agranular cortex (AGm), which is a subdivision of the medial prefrontal cortex (PFC) and has wide axonal connections with both cortical regions (including the posterior parietal cortex) and subcortical structures critical for attention/orientation processes. This study investigated whether the AGm is involved in attentional modulation of PPI. The results showed that PPI was enhanced by fear conditioning of the prepulse, and then further enhanced by perceived spatial separation between the conditioned prepulse and a back-ground masking noise based on the auditory precedence effect. Bilateral injection of 2-mM kynurenic acid, a broad spectrum antagonist of glutamate receptors, into the AGm, but not the primary somatosensory cortex, eliminated these two types of attentional enhancement of PPI. Thus, the AGm plays a role in facilitating attention to the prepulse and is involved in the top-down modulation of PPI.

Meng Q ，Ding Y ，Chen L ，Li L ... -  《-》

The effect of temporal predictability on sensory gating: Cortical responses inform perception.

Favero JD ，Luck C ，Lipp OV ，Marinovic W ... -  《-》