Roy Halliday

A low dose of subcutaneous nicotine improves information processing in non-smokers

Many studies have found that cigarette smoking or nicotine improves mental functioning in abstinent smokers. An unresolved issue is whether this improvement is due primarily to a direct facilitation of performance or to relief of the impairment caused by nicotine withdrawal. We evaluated the performance of 12 non-smokers before and twice (15 and 45 min) after a subcutaneous injection of 0.8 mg nicotine, 0.8 ml saline, and a control no treatment, on a choice reaction time (RT) task. Each treatment was given on a separate day; the control day was given on the first session. The order of nicotine and saline was balanced between subjects, and injections were given double-blind. The RT task manipulated stimulus and response processing. These manipulations consisted of two levels of stimulus complexity and two levels of response complexity, resulting in four task conditions. These manipulations along with latency measures of the event-related potential were used to identify the components of processing that mediated nicotines effects on performance. During each active drug session blood nicotine levels, cardiovascular, and subjective responses were measured before and after each of the three tests (pre-drug, 15 min and 45 min post-drug). For the information processing measures only the comparisons of the pre- and 15-min post-test showed significant drug effects. Nicotine compared to saline significantly increased the number of responses at the fast end of the RT distribution. However, there were no changes in accuracy. Nicotine also speeded mean RT compared with saline or the control day, but the effects were only significant for the control-nicotine comparison. There was an interaction between effects of nicotine and the task variables, such that nicotine speeded P3 latency in the hardest task condition, while slowing it in the other task conditions. Nicotine significantly increased heart rate, which lasted for the entire session. Blood nicotine levels were lower than expected from a preliminary study in smokers and may have been responsible for the smaller than expected mean RT effects. These findings suggest that even a low dose of nicotine directly affects attention or stimulus processing components of information processing. This study also illustrates the importance of assessing both multiple components of information processing and nicotine levels when examining the effects of nicotine on cognition.

Evoked potential variability: Effects of age, amplitude and methods of measurement ☆

Abstract Visual and auditory evoked potentials (EPs) were recorded from 120 children of 6–15 years of age. EP variability was measured using a variety of techniques. All of these techniques showed that variability decreased with increasing age. Similar measures applied to background EEG activity showed less adequate discrimination of age, suggesting that the effects observed are not entirely due to changes of background EEG activity. This contention is further supported by the polarity histogram measurement of variability, which indicates that variability of the late EP components (100 msec and later) decreases with increasing age more than does variability of earlier components. With some measures, variability is positively correlated with amplitude; with others, the correlations are negative. With all of the measures, variability is negatively correlated with age. This would indicate that the increasing EP stability with age is not a function of amplitude changes. These findings also illustrate some of the various EP variability measures available, how they relate to each other and how they are related to AEP amplitude.

Effects of oral scopolamine on human stimulus evaluation.

In a previous study of the effect of age on information processing, both age and stimulus complexity slowed reaction time (RT) and the latency of the P300 component of the brain event-related potential (ERP). The aim of the present study was to compare the effects of scopolamine (an anticholinergic) with the previously noted effects of age. The choice of scopolamine was prompted by current hypotheses concerning decline in cholinergic function with age.Twelve adult women were studied on a battery of tasks before and after scopolamine in oral doses of 0.0 (placebo), 0.6 and 1.2 mg. Reaction times (RT) and event-related potentials (ERP) were measured. The principal task was one that combined two levels of stimulus complexity and two levels of response difficulty to provide four subtasks. Scopolamine slowed RT and P300 as had age, but scopolamine slowed responses to simple stimuli more than responses to complex stimuli. Scopolamine effects on other tasks in the battery were small but consistent with an action of scopolamine on an early stimulus preprocessing stage that is independent of a stimulus evaluation stage that is also affected by age.

Cholinergic activity and constraints on information processing.

In humans, close relationships are found between cholinergic activity and constraints placed on information processing operations. This is true for all operations where the effects of cholinergic activity have been studied. Studies of vigilance, memory, problem solving, stimulus processing and response processing are cited as illustrations. These studies suggest the hypothesis that cholinergic activity controls constraints in all information processing operations. Alternative hypotheses are proposed and experimental tests are suggested.

The effect of methylphenidate on information processing

Models of information processing currently popular in cognitive psychology divide the reaction process into a series of discrete separable stages. The distinction between one stage and another is verified by the additive factors method (AFM) as defined by Sternberg (1969). Task factors that do not interact with each other are inferred to affect different stages. The distinction between stimulus evaluation stages and response selection stages has been supported by brain event related potential (ERP) studies. The latency of the P300 component of the ERP is sensitive to changes in stimulus complexity but not to to changes in response complexity. The focus of this research is to determine the effects of stimulant drugs on stages of information processing using both reaction time (RT) and P300 latency within an AFM framework. four doses of methylphenidate (MP) were used in a within-subjects design to examine the effects of MP on stimulus and response processing. We found that MP speeds RT, and that this effect does not interact with the effect of stimulus complexity on RT. MP dose interacts with response complexity, the dose for optimal speeding varying with the level of complexity. The latency of P300 is increased by stimulus complexity, and not by response complexity, nor is it affected by MP. These results show that the stimulant drug acts on processes involved in response selection, rather than in stimulus evaluation. Individual differences in drug response are dose dependent, but also point to an effect on response processing.

The effect of attentional effort on visual evoked potential N1 latency

The latency of the visual evoked potential N1 component evoked by nontarget stimuli increases with an increased attention to nontarget stimuli. The latency increase seems related to a general effort at processing, rather than any early filtering. This phenomenon is illustrated in one study of hyperactive children and another of normal young adults. The literature of this phenomenon is reviewed, and various explanations are considered. It does not appear to be a result of a slow negative wave, but rather a genuine effect of one aspect of attention on N1.

Visual evoked potential changes induced by methylphenidate in hyperactive children: Dose/response effects

Visual event related potentials (ERP) were recorded from 21 hyperactive children aged 7-13 years under two attention conditions at 4 levels of methylphenidate dose (placebo, low, medium and high). ERP measures were very sensitive to age (under or over 10 years) and attention condition, but less sensitive to drug dose. There appeared to be two classes of drug dose effect on ERP amplitude, those that changed monotonically with dose and those from which dose interacted with attention non-monotonically. Drug effect on ERP amplitude may also depend on age so that opposite effects may occur in young and old children. No latency measures showed a dose effect. It appears that methylphenidate can speed reaction times without shortening ERP latency. This suggests the drug acts more on response-related processes than on stimulus evaluation.

Time shipt evoked potentials (TSEPs): Method and basic results☆

A simple technique for generating averaged evoked potentials to auditory signals that appear to move in space is described. Shifts in the apparent location of the signal were created by digitally delaying the output of a white noise generator with a minicomputer. The two channels were reconverted to two analog signals and presented binaurally through headphones. Shifts inthe apparent location of the signal produced a time shifted evoked potential (TSEP) that was not present during monaural control runs. TSEP amplitudes were largest near the vertex and varied as a function of the presentation format.

Effects of two doses of methylphenidate on verbal information processing in hyperactive children

Nine hyperactive children participated in three sessions. During each they were given one of three drugs (placebo, 10 mg, or 21 mg of methylphenidate) in a double-blind crossover study. Following drug administration they were tested on three cognitive tasks. For one task, structural, acoustic, or semantic degrees of encoding of verbal information were induced. Memory for the verbal information was then tested. The 10-mg dose resulted in overall improvement of word recognition and recall. The 21-mg dose did not result in improvement. Amount of improvement was not related to degree of encoding of words. Two other tasks, learning a list of words and visual search of letters from a briefly presented display, were not affected by either the 10- or 21-mg dose. The results indicate that verbal learning can be facilitated by a low dose of methylphenidate but that the dose range may be narrow. Also, certain individuals did not respond favorably to either dose. In discussing the results, the possibility is presented that methylphenidate-induced facilitation may be restricted to certain types of learning or certain methods of assessing retrieval of information.

A comparison of methods for measuring event-related potentials.

Visual event-related potentials (ERPs) were recorded from 21 hyperactive children under 2 attention conditions and 4 doses of stimulant drug (methylphenidate). This data base was used to evaluate several methods of EP component measurement. These methods were (1) conventional visual peak and trough selection; (2) automatic feature extraction based on peaks; (3) automatic features extraction based on segments; (4) gross amplitude measures; (5) principal components analysis on normalized data and latency-adjusted data. No one method emerged as the best overall. Rather it is the case that different methods are best suited to different purposes, and criteria for choosing methods are outlined.