Neural Correlates of Attentional Modulation of Prepulse Inhibition

Prepulse inhibition (PPI) refers to the suppression of the startle reflex when the intense startling stimulus is shortly (20–500 ms) preceded by a weak non-startling stimulus (prepulse). Although the main neural correlates of PPI lie in the brainstem, previous research has revealed that PPI can be top-down modulated by attention. However, in the previous attend-to-prepulse PPI paradigm, only continuous prepulse but not discrete prepulse (20 ms) could elicit attentional modulation of PPI. Also, the relationship between the attentional enhancement of PPI and the changes in early cortical representations of prepulse signals is unclear. This study develops a novel attend-to-prepulse PPI task, when the discrete prepulse is set at 150 ms at a lead interval of 270 ms, and reveals that the PPI with attended prepulse is larger than the PPI with ignored prepulse. In addition, the early cortical representations (N1/P2 complex) of the prepulse show dissociation between the attended and ignored prepulse. N1 component is enhanced by directed attention, and the attentional increase of the N1 component is positively correlated with the attentional enhancement of PPI, whereas the P2 component is not affected by attentional modulation. Thus, directed attention to the prepulse can enhance both PPI and the early cortical representation of the prepulse signal (N1).

Pontine Omnipause Activity During Conjugate and Disconjugate Eye Movements in Macaques

Previous reports have shown that saccades executed during vergence eye movements are often slower and longer than conjugate saccades. Lesions in the nucleus raphe interpositus, where pontine omnipause neurons (OPNs) are located, were also shown to result in slower and longer saccades. If vergence transiently suppresses the activity of the OPNs just before a saccade, then reduced presaccadic activity might mimic the behavioral effects of a lesion. To test this hypothesis, 64 OPNs were recorded from 7 alert rhesus monkeys during smooth vergence and saccades with and without vergence. The firing rate of many OPNs was modulated by static vergence angle but not by version and showed transient changes during slow vergence without saccades. This modulation was smooth, and not the abrupt pause seen for saccades, indicating that OPNs do not act as gates for vergence commands. We confirmed that saccades made during both convergence and divergence are significantly slower and longer than conjugate saccades. OPNs paused for all saccades, and the pause lead (interval between pause onset and saccadic onset) was significantly longer for saccades with convergence, in agreement with our hypothesis. Contrary to our hypothesis, pause lead was not longer for saccades with divergence, even though these saccades were slowed as much as those occurring during convergence. Furthermore, there was no significant correlation, on a trial-by-trial basis, between pause lead and saccadic slowing. These results suggest that it is unlikely that presaccadic slowing of OPNs is responsible for the slower saccades seen during vergence movements.

Investigation of Threat-Related Attentional Bias in Anxious Children Using the Startle Eyeblink Modification Paradigm

We used the startle eyeblink modification paradigm to investigate whether clinically anxious children, like high trait-anxious adults, display a bias in favour of threat words compared to neutral words. The present study included 16 clinically anxious children whose diagnostic status was determined using the parent version of a semistructured diagnostic interview as part of a larger childhood anxiety study. The children were presented with threat and neutral words for 6 s each. A startle-eliciting auditory stimulus - a 100 dBA burst of white noise of 50 ms duration - was presented during the words at lead intervals of 60, 120, 240, or 3500 ms and during intertrial intervals. The overall pattern of startle eyeblink modification indicated inhibition at the 120 and 240 ms lead intervals and facilitation at the 3500 ms lead interval. Startle-latency shortening during threat words at the 60 ms lead interval was larger than at other intervals, whereas there was no difference during neutral words. This result reflects an anxiety-related bias in favour of threat words occurring at a very early - and possibly preattentive stage - of information processing.