Prestimulation-induced modulation of the P300 component of event related potentials accompanying startle in children.

Positive EEG deflections with the latency and scalp distribution of the P300 accompany startle in response to loud auditory stimuli in a non-task context. The purpose of this investigation is to determine if inhibitory and facilitatory prestimulation would have effects on the P300 similar to those on the startle blink. Prestimulation conditions were chosen to induce startle amplitude facilitation (4000 msec sustained tone), startle amplitude inhibition (120 msec prestimulation interval), and startle onset latency facilitation (60 msec prestimulation interval). Ninety-three boys (including normals and those with ADHD and/or enuresis) from a startle modulation study had EEG recordings of sufficient quality to provide data for the current study. Repeated measures analyses of variance demonstrated startle amplitude and P300 amplitude facilitation following the 4000 msec tone, startle amplitude and P300 amplitude inhibition following the 120 msec prestimulation interval, and startle onset latency and P300 peak latency facilitation (shorter latencies) following the 60 msec prestimulation interval. Hence, the vertex-recorded P300 elicited by startling stimuli was modulated by non-startling prestimulation in a manner that paralleled that of modulation of the brain-stem generated startle blink. Startle inhibition by prestimulation is mediated by an inhibitory pathway in the mesopontine lateral tegmentum. This brain-stem circuitry has a similar effect on the P300 even though the latter may be generated in more rostral structures. Alternatively, this automatically elicited P300 may represent a limbic or cortical reflection of the sensory processing taking place in the brain-stem. Either interpretation suggests a "bottom-up" as contrasted with a "top-down" mode of sensory processing. This P300 obeys the rules of startle modulation by brain-stem mechanisms rather than indexing cortical evaluation of stimuli for task relevance, stimulus probability, and prior uncertainty.

Maturation of prestimulation-induced startle modulation in girls.

This study of the maturation of prestimulation-induced modulation of startle in 4- to 8-year-old girls and young women demonstrated significant effects of age on both startle amplitude and onset latency modulation. Prestimulation with nonstartling tones resulted in strong inhibition of both amplitude and latency of the startle blink reflex in adults when 25-ms tones preceded the startling stimuli by 120 ms or 250 ms. Following sustained prestimulation for 2000 ms, the adults showed weak nonsignificant response facilitation. Eight-year-old girls showed mature inhibitory startle amplitude modulation, but significantly less inhibition of onset latency compared to adults. Preschool girls showed significantly less amplitude and latency inhibition and more facilitation than 8-year-olds and adult women. These findings in female subjects were very similar to those obtained by Ornitz, Guthrie, Kaplan, Lane, and Norman (1986) in male subjects. Gender differences were limited to the 8-year-old age group. The 8-year-old girls showed significantly less startle amplitude inhibition than 8-year-old boys following the 120-ms and 250-ms prestimulation intervals and less latency facilitation following 2000 ms of sustained prestimulation. In general, these findings suggest that brainstem mechanisms that mediate startle response modulation undergo development during early childhood and do not mature until about 8 years of age in both male and female subjects. The results are discussed in relation to studies of gender effects on development of other neurophysiological variables and to maturation of the nervous system.

Anxiolytic effects of smoking associated with four stressors.

There is a widespread belief that cigarette smoking alleviates stress. The literature reveals conflicting results on the anxiolytic effects of smoking. This study was designed to replicate a report that smoking (a) reduced subjective anxiety induced by stressful anagrams and (b) increased pain threshold for a cold pain task. This study (N = 15) included two other stressors: white noise and an auditory vigilance task. A significant Time x Condition (smoking vs. deprived) interaction was found for Spielberger State Anxiety Inventory scores in the anagram task. A borderline significant interaction effect was found for the cold pain task. No significant effects were found with the two other tasks. These results provide partial support for the popular notion that smoking mitigates stress-induced anxiety. No difference was found between the smoking and deprived conditions for either pain threshold or pain endurance.