Reaction Time Latency Research Articles

Do Episodic Migraineurs Selectively Attend to Headache‐Related Visual Stimuli?

To assess pain-related attentional biases among individuals with episodic migraine. Prior studies have examined whether chronic pain patients selectively attend to pain-related stimuli in the environment, but these studies have produced largely mixed findings and focused primarily on patients with chronic musculoskeletal pain. Limited research has implicated attentional biases among chronic headache patients, but no studies have been conducted among episodic migraineurs, who comprise the overwhelming majority of the migraine population. This was a case-control, experimental study. Three hundred and eight participants (mean age = 19.2 years [standard deviation = 3.3]; 69.5% female; 36.4% minority), consisting of 84 episodic migraineurs, diagnosed in accordance with International Classification of Headache Disorders (2(nd) edition) criteria using a structured diagnostic interview, and 224 non-migraine controls completed a computerized dot probe task to assess attentional bias toward headache-related pictorial stimuli. The task consisted of 192 trials and utilized 2 emotional-neutral stimulus pairing conditions (headache-neutral and happy-neutral). No within-group differences for reaction time latencies to headache vs happy conditions were found among those with episodic migraine or among the non-migraine controls. Migraine status was unrelated to attentional bias indices for both headache (F [1,306] = 0.56, P = .45) and happy facial stimuli (F [1,306] = 0.37, P = .54), indicating a lack of between-group differences. Lack of within- and between-group differences was confirmed with repeated measures analysis of variance. In light of the large sample size and prior pilot testing of presented images, results suggest that episodic migraineurs do not differentially attend to headache-related facial stimuli. Given modest evidence of attentional biases among chronic headache samples, these findings suggest potential differences in attentional processing between chronic and episodic headache subforms.

Acute effects of whole body vibration on directionality and reaction time latency of trunk muscles: The importance of rest and implications for spine stability

Workplace exposure to whole body vibration (WBV) has been identified as one of the major physical risk factors encountered by the population. There are indications that, subsequent to a perturbation, impaired reflex response could allow for destabilization of the spine, possibly leading to injury. The purpose of this study was to investigate if WBV alters reflex response of trunk muscles and if the direction of perturbation (flexion or extension or lateral) and delay between exposure and perturbation influences the response. The results indicate that EMG latency was increased more in the vibration condition than in sitting without vibration. Significant effects with respect to directionality were observed in Erector Spinae muscles. The EMG latency reduced from the effect of perturbation after a 20s rest period. Even though the EMG latency did not fully return to its Pre-test state, the present results still show that recovery from the acute effects of WBV is possible with a rest period.

Comparison of 6‐hydroxydopamine lesions of the substantia nigra and the medial forebrain bundle on a lateralised choice reaction time task in mice

Parkinson's disease is most commonly modelled via unilateral infusion of the neurotoxin 6-hydroxydopamine (6-OHDA) in the rat, but recent work has been aimed to translate the reproducibility and reliability of the model to the mouse. Here we present the effects of unilateral 6-OHDA lesions to either the medial forebrain bundle or the substantia nigra (SN) in mice, which were trained on a lateralised choice reaction time (RT) task. This task measures response accuracy as well as RT and movement time latencies, and offers the opportunity for a more fine-grained analysis of the precise nature of the movement deficit, motor learning and functional recovery than can be achieved using classical tests of simple motor asymmetry. Both lesion types caused impaired response accuracy, which was more pronounced when responses had to be directed contralateral to the lesion. Furthermore, movement times were increased for both lesion groups, whereas only the bundle lesion group displayed a RT deficit. The lesions were stable over three consecutive weeks of testing, therefore lesion-type and behavioural assessment on the operant task are suitable to investigate the dopaminergic system in parkinsonian mice. Both lesions were stable over time, and were more pronounced when responses were directed in contralateral space; the mice with more complete bundle lesions displayed a greater deficit than mice that received lesions to the SN. The translation of this choice RT task will be beneficial for the assessment of therapeutics in mouse models of the disease.

Characterisation of spatial neglect induced by unilateral 6-OHDA lesions on a choice reaction time task in rats

Unilateral dopamine depletion and excitotoxic lesions of the striatum have been shown to induce a contralateral neglect when rats have to respond in a choice reaction time setting. Whereas, in a lateralised setting when response options are to either side of the animal's head all contralateral responding is impaired, testing animals only on one side of the head per day but with a near and far response option, rats are able to correctly respond to contralateral stimuli, but rather bias their responses towards the near hole. Here, we further investigated the nature of the contralateral neglect in egocentric space coding in more detail. Firstly, we tested the effects of near-complete unilateral dopamine depletion on this type of task. Secondly, previous observations suggested that lesioned rats shifted their response strategy which resulted in a response bias towards the most proximal location in contralateral space. In order to “encourage” dopamine depleted rats to respond to the neglected response location we implemented an error correction procedure to the task. Near-complete unilateral dopamine depletion, via 6-hydroxydopamine infusions into the medial forebrain bundle of female Lister Hood rats, resulted in a reduction of usable trials, a near hole bias when animals were tested on the side contralateral to the lesion, as well as increased reaction and movement time latencies. The introduction of an error-correction procedure had no effect on the animals’ response bias towards the near contralateral location. Probe trials showed that the bias is most likely the result of responses being misdirected when in a choice situation. The findings further highlight the role of dopamine and an intact striatum to code responses into egocentrically defined space.

Dynamic characteristics of multisensory facilitation and inhibition

Multimodal integration, which mainly refers to multisensory facilitation and multisensory inhibition, is the process of merging multisensory information in the human brain. However, the neural mechanisms underlying the dynamic characteristics of multimodal integration are not fully understood. The objective of this study is to investigate the basic mechanisms of multimodal integration by assessing the intermodal influences of vision, audition, and somatosensory sensations (the influence of multisensory background events to the target event). We used a timed target detection task, and measured both behavioral and electroencephalographic responses to visual target events (green solid circle), auditory target events (2kHz pure tone) and somatosensory target events (1.5±0.1mA square wave pulse) from 20 normal participants. There were significant differences in both behavior performance and ERP components when comparing the unimodal target stimuli with multimodal (bimodal and trimodal) target stimuli for all target groups. Significant correlation among reaction time and P3 latency was observed across all target conditions. The perceptual processing of auditory target events (A) was inhibited by the background events, while the perceptual processing of somatosensory target events (S) was facilitated by the background events. In contrast, the perceptual processing of visual target events (V) remained impervious to multisensory background events.

Analgesic and anticonvulsant activity of new derivatives of 2-substituted 4-hydroxybutanamides in mice

AbstractEarlier in vitro studies of the compounds marked as GT27, GT28, GT29 and BM128 revealed their inhibitory action towards murine γ-aminobutyric acid (GABA) transporters (mGAT1–mGAT4). In the present paper, the pharmacological activity of four γ-hydroxybutyric acid (GHB) amide derivatives was investigated. The following procedures were involved: locomotor activity, hot plate and electroconvulsive threshold tests. The compounds’ influence on motor coordination was evaluated in the chimney test, as well. Intraperitoneal (ip) administration of the GHB derivatives decreased animals’ locomotor activity (ED50 values ranged between 23.79 and 26.37mg/kg). At a dose of 25mg/kg (ip) the compounds prolonged the nociceptive reaction time latency in the hot plate assay to various degree and GT28 and GT29 were the most potent ones in this respect. Their analgesic efficacy was particularly pronounced 30min after their administration [percent of maximal possible effect (%MPE) = 16.93 and 22.72, respectively]. The investigated GHB derivatives, except for GT29 at 100mg/kg, increased the electroconvulsive threshold by approximately 4–11 mA as compared to the vehicle-treated mice. In the chimney test they impaired the animals’ motor coordination to various degree. We suggest further investigations of the compounds to estimate their biological activity.

Catching of Balls Unexpectedly Thrown or Fired by Cannon

Although learned actions can be automatically elicited in response to expected stimuli for which they have been prepared, little is known about whether learned actions can be automatically initiated by unexpected stimuli. Responses of unwitting participants to balls unexpectedly thrown by an experimenter (n=10) or propelled by a hidden ball cannon (n=22) were recorded by motion capture. Experience of ball catching correlated negatively with hand movement distance, indicating most responses were defensive, but successful catches were made in response to both thrown and fired balls. Although reaction time was faster in response to fired balls, interception was more frequent in response to thrown balls, indicating that movement cues by the thrower facilitated unexpected ball catching. The latency to begin a catching action by the only successful catcher of an unexpectedly fired ball was 296 msec. Given current knowledge of reaction time tasks and latencies of neural substrates of conscious perception and deliberation, it is probable that there was insufficient time available for conscious preparation of catch attempts. Ball catching may represent an example of a learned response which can be rapidly and unconsciously initiated without contextual priming or expectation of the stimulus.

Aerobic Fitness and Intra-individual Variability on Neurocognitive Function in Preadolescent Children

Increased intra-individual variability of task performance is associated with age-related cognitive decline and several diseases including schizophrenia, neurodegenerative disorders, and traumatic brain injury. Given the positive relation of aerobic fitness to cognition in children, a better understanding of the extent to which fitness relates to brain health and cognitive variability during development is of interest. PURPOSE: To determine the relation of aerobic fitness to intra-individual variability during childhood and to examine whether variability of neuroelectic parameters reflect differential cognitive control. METHODS: 93 children (39 female; range: 8-10 years) were recruited. Event-related potentials and task performance were subsequently measured during compatible and incompatible stimulus-response conditions of a modified flanker task that modulates attention and inhibition. This task modulates perceptual difficulty through congruency of target and non-target stimuli, as well as response compatibility through the manipulation of stimulus-response mappings. Intra-individual variability was characterized by computing standard deviation and ex-Gaussian parameters (mu, sigma, tau) for P3 amplitude and latency, and reaction time. RESULTS: Findings indicated that the compatible, relative to the incompatible, condition was associated with less intra-individual variability in reaction time, P3 amplitude, and P3 latency. Further, the congruent conditions, relative to the incongruent conditions, were associated with less intra-individual variability in reaction time and P3 latency. With regard to fitness, higher fitness was associated with shorter and less variable reaction time only for the incompatible condition, with no fitness-related differences observed for the P3 component. CONCLUSION: These findings suggest that tasks requiring greater cognitive control demands are associated with increased intra-individual variability. Findings also support previous research suggesting that higher amounts of fitness are associated with greater integrity of cognitive control and indicate that fitness-related differences in intra-individual variability occur after stimulus engagement and before response execution. Supported by NICHD Grant R01 HD055352

Reaction Time Variability in HIV-Positive Individuals

Progression of HIV/AIDS is frequently associated with frontal/subcortical dysfunction and mean reaction time (RT) slowing. Beyond group means, within-subject variability of RT has been found to be particularly sensitive to frontal/subcortical dysfunction in other populations. However, the possible relevance of RT variability to HIV/AIDS patients remains unknown. This study evaluated the relationships between RT variability and indicators such as neurocognitive, behavioral, and immunological status. A total of 46 HIV-positive adults on antiretroviral medication regimens were included in this study. Overall performance of this sample was poorer than normative means on measures of RT latency, RT variability, and traditional neurocognitive domains. Results demonstrated that the measures of RT variability were associated with global cognition, medication adherence rates, and peak immunological dysfunction, above and beyond the effects of RT latency. These preliminary findings suggest that measures of RT variability may provide enhanced sensitivity to neurocognitive disease burden in HIV/AIDS relative to more traditional measures of mean RT or cognitive function.

Role of the premotor cortex in leg selection and anticipatory postural adjustments associated with a rapid stepping task in patients with stroke

The premotor cortex (PMC) plays an important role in selecting and preparing for movement. This study investigates how stroke-induced PMC lesions affect stepping leg selection and anticipatory postural adjustments (APAs) preparation. Fifteen hemi-paretic patients (eight with PMC lesions (PMC Lesion) and seven PMC spared (PMC Spared)) and eight age- and sex-matched healthy adults participated in the study. The subjects performed rapid forward stepping with the right or left leg under simple and choice reaction time conditions. The percentage of trials in which the subject showed the correct initial vertical ground reaction force pattern before lift-off of the stepping leg indicated the accuracy in selecting the designated stepping leg. The latency of bilateral contractions in the tibialis anterior (TA) and the reaction time (RT) of the stepping leg represented the time needed to prepare for stepping-related APAs and stepping movement, respectively. All three groups demonstrated a similar rate of accuracy of the stepping leg selection under both conditions. However, in both conditions, the PMC Lesion group exhibited a longer RT and TA contraction latency of the affected leg than the healthy and PMC Spared groups. The PMC Lesion group also presented a longer TA contraction latency of the unaffected leg than the healthy group in both conditions. These results suggest that the PMC is involved in APAs associated with leg stepping movement and that a PMC lesion in one hemisphere impairs APAs of both the contralateral and ipsilateral legs during stepping.

Sensitivity of continuous performance test (CPT) at age 14 years to developmental methylmercury exposure

Hit Reaction Time latencies (HRT) in the Continuous Performance Test (CPT) measure the speed of visual information processing. The latencies may involve different neuropsychological functions depending on the time from test initiation, i.e., first orientation, learning and habituation, then cognitive processing and focused attention, and finally sustained attention as the dominant demand. Prenatal methylmercury exposure is associated with increased reaction time (RT) latencies. We therefore examined the association of methylmercury exposure with the average HRT at age 14 years at three different time intervals after test initiation. A total of 878 adolescents (87% of birth cohort members) completed the CPT. The RT latencies were recorded for 10 min, with visual targets presented at 1000 ms intervals. After confounder adjustment, regression coefficients showed that CPT-RT outcomes differed in their associations with exposure biomarkers of prenatal methylmercury exposure: During the first 2 min, the average HRT was weakly associated with methylmercury (beta (SE) for a ten-fold increase in exposure, (3.41 (2.06)), was strongly for the 3-to-6 min interval (6.10 (2.18)), and the strongest during 7–10 min after test initiation (7.64 (2.39)). This pattern was unchanged when simple reaction time and finger tapping speed were included in the models as covariates. Postnatal methylmercury exposures did not affect the outcomes. Thus, these findings suggest that sustained attention as a neuropsychological domain is particularly vulnerable to developmental methylmercury exposure, indicating probable underlying dysfunction of the frontal lobes. When using CPT data as a possible measure of neurotoxicity, test results should therefore be analyzed in regard to time from test initiation and not as overall average reaction times.

Brain activity during processing objects and pseudo-objects: Comparison between adult regular and dyslexic readers

Objective The role of visual processing deficits in dyslexia remains unclear and continues to stir controversy. Most studies to date have used alphabetic and or other language-dependent patterns. The current study compares how dyslexics and regular readers process non-alphabetic visual patterns. Methods The stimuli were black and white drawings, 50 meaningful (concrete objects) and 50 meaningless (pseudo-objects with no linguistic name) presented visually on a computer screen. Measures included behavioral accuracy and reaction time, event-related potential (ERP), and low resolution electromagnetic tomography (LORETA). The subjects were 15 dyslexic and 15 aged-matched regular readers. Results The dyslexics exhibited significantly longer reaction time and shorter latencies of P1 and P2 components to both objects and pseudo-objects compared to the regular readers. Data from the LORETA solution analysis indicated significantly different brain activity between the two groups: both exhibited higher left hemisphere activation when viewing objects compared to pseudo-objects; and dyslexics exhibited lower left hemisphere activation when viewing objects and higher right hemisphere activation when viewing pseudo-objects during the early stages of processing. Conclusions The results support the notion that brain activation of dyslexic readers differs from that of the regular readers when processing non-alphabetic patterns, and that the differences appear from the early stage of processing. Significance These results emphasize that differences in brain activity between dyslexic and regular readers can be seen even in a non-alphabetic task, and in early stages of processing.

Effect of Mastication on Human Brain Activity

Mastication is a complicated movement generated from a neural population in the brainstem and a neural network involving several brain regions. Recently, attention has been focused on the relationship between mastication and age-related decline in human cognitive function, but the neural mechanisms underlying this association remain unknown. In this article, we review research on the effect of mastication based on data obtained using event-related potentials (ERPs), including the P300 component and contingent negative variation (CNV), motor-related cortical potentials (MRCPs), and reaction time (RT) as behavioral data. The peak latency of P300 and RT clearly shortened with the repetition of sessions in Mastication, but not in Control, Jaw Movement, or Finger Tapping. The mean amplitude of CNV differed between the Mastication and Control conditions with the repetition of sessions. By contrast, there was no significant difference in the amplitude of MRCP between Mastication and Control in any of the sessions. These results suggest that mastication is associated with cognitive processing rather than movement-related processing in the human brain. We believe that non-invasive recording methods, such as electroencephalography (EEG), magnetoencephalography (MEG), transcranial magnetic stimulation (TMS), functional magnetic resonance imaging (fMRI), and near-infrared spectroscopy (NIRS), will supply valuable evidence in support of a positive relationship between mastication and cognition.

Sensitivity of Continuous Performance Test (CPT) to Methylmercury Exposure at Age 14 Years

ISEE-0186 Background and Objectives: Reaction Time latencies (RT) measured in the Continuous Performance Test (CPT) indicate the speed of information processing. The latencies may be related to different neuropsychological functions depending on the time intervals during the test duration when the responses are assessed: 1-2 minutes with orientation, learning and habituation; the following few minutes with cognitive speed of processing in selective focused attention; and a final period with sustained attention as the dominant demand. Prenatal methylmercury exposure has been associated with increased reaction time latencies at age 7 years in Faroese children. We assessed the association of methylmercury exposure with the average RT in three time intervals at age 14 years. Methods: Exposure levels were determined from mercury concentrations in cord blood, postnatal blood, and hair samples from a Faroese cohort. 878 children completed CPT. RT latencies were recorded during 10 minutes test duration on a task of target stimuli. Regression models were adjusted for confounders. Results: The three sets of CPT-RT outcomes showed different association patterns with methylmercury exposure: the average RT for the first 1-2 minutes was weakly associated with methylmercury (Beta (SE), 2.83 (2.10)); a significant association for the 3-6 minute interval (4.95 (2.23)); and a strongest association for the 7-10 minutes (6.41 (2.45)). This association pattern was unchanged when the scores of Catsys-Reaction Time Test, Finger Tapping Test or CPT-RT (1-2 minutes) were included in the models as confounders to control for simple reaction time and characteristics of learning. No association was found in regard to measures of postnatal exposures. Conclusion: The CPT-RT latencies reflect different functions, as indicated by results separated according to test duration. The findings show that neuropsychological functions related with sustained attention are particularly vulnerable, indicating probable underlying dysfunctions of frontal lobes. This association may be missed, if test results are averaged.

Effect of Omega-3 and Policosanol Supplementation on Attention and Reactivity in Athletes

Objective: The purpose of this study was to determine the effect of omega-3 fatty acids and policosanol supplementation on the cognitive processes involved in the control of reactivity in karateka engaged in attention tests.Methods: Eighteen karateka were randomly assigned to 2 groups. One group (10 subjects) took the supplement of omega-3 fatty acids (2.25 g) plus policosanol (10 mg) (O3 + P) for 21 days, and the other group was supplemented with placebo (oleic sunflower oil). Subjects were tested at the beginning of the experiment (Test 1), after 21 days (Test 2), and after 42 days (Test 3). The experimental procedure consisted of an Alert and a Sustained Attention (SA) reaction time test: the subject had to react by pressing a key of a computer keyboard in Alert and a sequence of 3 keys in SA in response to stimuli, activating a complex go/no-go paradigm. For each test, we recorded the reaction time and the event-related potentials by electroencephalogram and electromyography (EMG) of the forefinger flexor muscle. The Profile of Mood States (POMS) test was also administered.Results: After 21 days of supplementation, subjects who received O3 + P showed a reduced reaction time and increased vigor sensation associated with a reduction of the negative states measured with the POMS test. Analysis of the event-related brain potentials showed a reduced latency of the movement-related brain macropotentials. In particular, the potentials recorded in the premotor period and motor period occurred earlier and the latency of EMG activation was reduced. In the third test, 21 days after the last O3 + P supplementation, the positive effects on the mood state persisted, while the reaction time, EMG, and brain potential latencies increased, although their values remained lower than in the first test. The placebo group did not show any significant differences in Tests 2 and 3 compared to Test 1 for either POMS or reactivity and brain potentials.Conclusions: Supplementation with O3 + P may be effective in improving mood state and reactivity. The reaction time reduction appears to be due to a central nervous system effect, as shown by the reduced latency of movement-related brain macropotentials and EMG activation. These results are in line with previous experiments.

Visuospatial asymmetry and non-spatial attention in subacute stroke patients with and without neglect

Asymmetry in performance and an association with non-lateralized attention are often mentioned as two important aspects of the clinical manifestation of visuospatial neglect. Both these aspects were investigated in 21 left (LH) and 24 right hemisphere (RH) stroke patients and in 20 healthy subjects. The letter and star cancellation subtests of the Behavioural Inattention Task (BIT) and a computerized visual reaction time task (CVRT) with stimuli presented either left, central or right in extrapersonal space were administered. In LH patients, the calculation of BIT asymmetry scores allowed a better distinction between patients with and without neglect than raw omission scores. However, in RH patients, raw and asymmetry scores led to similar classifications. In the CVRT, raw and asymmetry scores for the number of omissions also produced identical classifications. Thus, the computation of asymmetry scores for omissions did not substantially refine the diagnosis of neglect. On the other hand, more patients were classified as neglect patients by using CVRT reaction time (RT) asymmetry scores than by using BIT or CVRT omission scores. Ipsilesional RT's were chosen as a measure of general, non-lateralized attention. The ipsilesional RT's of the LH and RH patients did not differ from the healthy subjects' lateral RT's. However, within the RH group, patients with both RT asymmetries and BIT scores above cut-off level showed longer ipsilesional RT's than patients with defective RT asymmetries but normal BIT scores. This supports the idea of an interaction between lateralized and non-lateralized attentional components in neglect, in which the presence of general attentional deficits exacerbates the severity of neglect symptoms. RT tasks may contribute to the detection of asymmetries in visuospatial attention in patients with subclinical neglect symptoms, who might compensate for their lateralized deficit in paper-and-pencil tasks employing intact general attention.

Precues enable multiple response preprogramming: Evidence from startle

When one or more response dimensions in a choice reaction time (RT) task are provided beforehand (or precued), RT decreases, indicating that the precued part of a response was prepared in advance. In this study, a startling acoustic stimulus was used to investigate the amount of preprogramming that occurs when part of the response is precued because a startling stimulus has been shown to directly trigger preprogrammed responses. Participants performed wrist flexion/extension movements in a precued one to four choice RT paradigm. A control auditory stimulus (82 dB) or a startling acoustic stimulus (124 dB) accompanied the visual "go" signal on each trial. Although RT latencies were significantly reduced by the startle, many more errors were observed in the startled conditions. Importantly, the errors seen at short RT latencies largely reflected multiple movements to the cued response alternatives, suggesting that multiple responses were preprogrammed.

General physical activity levels influence positive and negative priming effects in young adults

To investigate the relationship between general physical activity level and the cognitive functions of executive control in young adults using behavioral measures and event-related brain potentials. Forty young adults (mean age=21.1 yrs; 19 females) were differentiated on the basis of their regular physical activity level into two groups: active and sedentary. They performed a spatial priming task consisting of three conditions: control, positive, and negative priming. Spatial priming effects, which are related to executive control and occur automatically, were assessed as indicators of cognitive functioning. Negative priming effects on reaction time and P3 latency in the active group were larger than in the sedentary group. By contrast, positive priming effects were only observed in the sedentary group. The cognitive effects of regular physical activity could be observed using a relatively simple paradigm. The results indicate that regular physical activity has a beneficial effect on the cognitive processes on executive control in young adults. The present study provides additional evidence of the beneficial effects of regular physical activity on cognitive functioning in young adults.

Early, untreated Parkinson's disease patients show reaction time variability

While Parkinson's disease (PD) is associated with motor slowing, less attention has been paid to variability in performance on motor and cognitive tasks. To examine reaction time latencies and intraindividual variability in untreated patients with PD compared to healthy controls. Twenty-nine (19 men/10 women) patients with untreated PD and 16 controls (8 men/8 women) were examined using measures of simple reaction time (SRT) and choice reaction time (CRT) in addition to cognitive measures of executive function (Trail Making Test; adaptive digit ordering). Latencies and intraindividual variability were compared between groups. Partial correlation coefficients, adjusting for age, sex and education were used to examine the relationship between RT measures and motor or cognitive measures. Patients and controls did not differ with respect to age or sex distribution. Education and cognitive status differed between groups, but no subject was demented or clinically depressed. After adjusting for age, sex and education, significant group differences were found in latencies (2-choice RT and 8-choice RT) and intraindividual variability scores (all CRT conditions). Latencies did not differ significantly after adjusting for finger tapping rate. In the PD group neither the motor nor the executive measures correlated significantly with any of the reaction time measures. We conclude that CRT intraindividual variability and latencies are increased in untreated PD.

Effects of atomoxetine and methylphenidate on performance of a lateralized reaction time task in rats

The ability to detect unpredictable cues can involve stimulus-elicited orienting of attention (bottom-up processing); however, in many settings, target onset is partially predictable, meaning that subjects can benefit from the rule-guided, endogenous control of attention (top-down processing). Noradrenaline has been implicated in attention per se, but it is not clear whether it differentially participates in these two dimensions of attentional function. We sought to examine the effects of selective or nonselective inhibitors of noradrenaline reuptake on different modes of attentional performance in rats. Adult male Long-Evans rats were trained to perform a lateralized reaction time task where a variable-duration preparatory period preceded delivery of a visual target stimulus. Atomoxetine (1 mg/kg, i.p.) or methylphenidate (0.32 mg/kg, i.p.) were administered before sessions in which the preparatory period was systematically varied. When the preparatory time was brief (0.2 s), response times were significantly longer than when the preparatory time was long (1.0 s), suggesting that rats were able to orient their attention before target onset when the longer period was imposed. Atomoxetine differentially modulated performance in these two conditions, improving response accuracy when a long preparatory period was imposed but impairing accuracy when the preparatory time was made brief. Methylphenidate did not differentially affect responding under the two conditions. These data suggest that selective inhibition of the noradrenaline transporter may specifically benefit attentional performance of tasks that permit the controlled recruitment of attention, rather than during tests of pure stimulus-driven attention.