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 role of the deeper layers of the superior colliculus in attentional modulations of prepulse inhibition.

Prepulse inhibition (PPI) is the suppression of the startle reflex, when a weaker non-startling sensory stimulus (the prepulse) precedes the intense startling stimulus. Although the basic PPI neural circuitry resides in the brainstem, PPI can be enhanced by selective attention to the prepulse, indicating that this sensorimotor-gating process is influenced by higher-order perceptual/cognitive processes. Along with the auditory cortex, the brain structures involved in attentional modulations of PPI include both the lateral nucleus of the amygdala (LA), which contributes to the fear-conditioning modulation, and the posterior parietal cortex (PPC), which contributes to the spatially attentional modulation. The deeper layers of the superior colliculus (DpSC), which has been suggested as a midbrain component in the PPI circuitry, receive descending axonal projections from some forebrain structures associated with auditory perception, emotional conditioning, or spatial attention. This study was to examine whether the DpSC are also involved in attentional modulations of PPI in rats. The results showed that both fear conditioning of a prepulse sound and precedence-effect-induced perceptual separation between the conditioned prepulse and a noise masker facilitated selective attention to the prepulse and consequently enhanced PPI. Reversibly blocking glutamate receptors in the DpSC with 2-mM kynurenic acid eliminated both the conditioning-induced and the perceptual-separation-induced PPI enhancements. However, the baseline magnitudes of startle and PPI were not affected. The results suggest that the DpSC play a role in mediating the attentional enhancements of PPI, probably through both receiving top-down signals from certain forebrain structures and modulating the midbrain representations of prepulse signals.

Ding Y ，Xu N ，Gao Y ，Wu Z ，Li L ... -  《-》

Differentially organized top-down modulation of prepulse inhibition of startle.

Du Y ，Wu X ，Li L 《-》

Perceived location specificity in perceptual separation-induced but not fear conditioning-induced enhancement of prepulse inhibition in rats.

Prepulse inhibition (PPI) is the suppression of the startle reflex when the startling stimulus is shortly preceded by a non-startling stimulus (the prepulse). Previous studies have shown that both fear conditioning of a prepulse and precedence-effect-induced perceptual separation between the conditioned prepulse and a noise masker facilitate selective attention to the prepulse and consequently enhance PPI with a remarkable prepulse-feature specificity. This study investigated whether the two types of attentional enhancements of PPI in rats also exhibit a prepulse-location specificity. The results showed that when a prepulse was delivered by each of the two spatially separated loudspeakers, fear conditioning of the prepulse at a particularly perceived location (left or right to the tested rat) enhanced PPI without exhibiting any perceived-location specificity. However, when a noise masker was presented, the precedence-effect-induced perceptual separation between the conditioned prepulse and the noise masker further enhanced PPI when the prepulse was perceived as coming from the location that was conditioned but not the location without being conditioned. Moreover, both conditioning-induced and perceptual separation-induced PPI enhancements were eliminated by extinction learning, whose effect could be blocked by systemic injection of the selective antagonist of metabotropic glutamate receptor subtype 5 (mGluR5), 2-methyl-6-(phenylethynyl)-pyridine (MPEP). Thus, fear conditioning of a prepulse perceived at a particular location not only facilitates selective attention to the conditioned prepulse but also induces a learning-based spatial gating effect on the spatial unmasking of the conditioned prepulse, leading to that the perceptual separation-induced PPI enhancement becomes perceived-location specific.

Lei M ，Luo L ，Qu T ，Jia H ，Li L ... -  《-》

Spatial specificity in attentional modulation of prepulse inhibition of the startle reflex in rats.

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