Collicular dysfunction in attention deficit hyperactivity disorder

Seeing is believing: Larger Colavita effect in school-aged children with attention-deficit/hyperactivity disorder

Attention-deficit/hyperactivity disorder (ADHD) is a common neurodevelopmental disorder that leads to visually relevant compensatory activities and cognitive strategies in children. Previous studies have identified difficulties with audiovisual integration in children with ADHD, but the characteristics of the visual dominance effect when processing multisensory stimuli are not clear in children with ADHD. The current study used the Colavita paradigm to explore the visual dominance effect in school-aged children with ADHD. The results found that, compared with typically developing children, children with ADHD had a higher proportion of "visual-auditory" trials and a lower proportion of "simultaneous" trials. The study also found that the proportion of visual-auditory trials in children with ADHD decreased as their Swanson, Nolan, and Pelham-IV rating scale (SNAP-IV) inattention scores increased. The results showed that school-aged children with ADHD had a larger Colavita effect, which decreased with the severity of inattentive symptoms. This may be due to an overreliance on visual information and an abnormal integration time window. The connection between multisensory cognitive processing performance and clinical symptoms found in the current study provides empirical and theoretical support for the knowledge base of multisensory and cognitive abilities in disorders.

A novel intervention for treating adults with ADHD using peripheral visual stimulation

Objective

Stimulation of the peripheral visual field has been previously reported as beneficial for cognitive performance in ADHD. This study assesses the safety and efficacy of a novel intervention involving peripheral visual stimuli in managing attention deficit hyperactivity disorder (ADHD).

Methods

One hundred and eight adults, 18-40 years old, with ADHD, were enrolled in a two-month open-label study. The intervention (i.e., Neuro-glasses) consisted of standard eyeglasses with personalized peripheral visual stimuli embedded on the lenses. Participants were assessed at baseline and at the end of the study with self-report measures of ADHD symptoms (the Adult ADHD Self-Report Scale; ASRS), and executive functions (The Behavior Rating Inventory of Executive Function Adult Version; BRIEF-A). A computerized test of continuous performance (The Conners' Continuous Performance Test-3; CPT-3) was tested at baseline with standard eyeglasses and at the end of study using Neuro-glasses. The Clinical Global Impression-Improvement scale (CGI-I) was assessed at the intervention endpoint. Safety was monitored by documentation of adverse events.

Results

The efficacy analysis included 97 participants. Significant improvements were demonstrated in self-reported measures of inattentive symptoms (ASRS inattentive index; p = 0.037) and metacognitive functions concerning self-management and performance monitoring (BRIEF-A; p = 0.029). A continuous-performance test (CPT-3) indicated significant improvement in detectability (d'; p = 0.027) and reduced commission errors (p = 0.004), suggesting that the Neuro-glasses have positive effects on response inhibition. Sixty-two percent of the participants met the response criteria assessed by a clinician (CGI-I). No major adverse events were reported.

Conclusion

Neuro-glasses may offer a safe and effective approach to managing adult ADHD. Results encourage future controlled efficacy studies to confirm current findings in adults and possibly children with ADHD.Clinical trial registration: https://www.clinicaltrials.gov/, Identifier NCT05777785.

The Superior Colliculus: Cell Types, Connectivity, and Behavior

The superior colliculus (SC), one of the most well-characterized midbrain sensorimotor structures where visual, auditory, and somatosensory information are integrated to initiate motor commands, is highly conserved across vertebrate evolution. Moreover, cell-type-specific SC neurons integrate afferent signals within local networks to generate defined output related to innate and cognitive behaviors. This review focuses on the recent progress in understanding of phenotypic diversity amongst SC neurons and their intrinsic circuits and long-projection targets. We further describe relevant neural circuits and specific cell types in relation to behavioral outputs and cognitive functions. The systematic delineation of SC organization, cell types, and neural connections is further put into context across species as these depend upon laminar architecture. Moreover, we focus on SC neural circuitry involving saccadic eye movement, and cognitive and innate behaviors. Overall, the review provides insight into SC functioning and represents a basis for further understanding of the pathology associated with SC dysfunction.

Impaired Local and Long-Range Brain Connectivity and Visual Response in a Genetic Rat Model of Hyperactivity Revealed by Functional Ultrasound

Attention-Deficit hyperactivity disorder (ADHD) is a central nervous system (CNS) disorder frequently associated with other psychiatric disorders. Pathophysiology processes at stake in ADHD are still under investigation and interestingly neuroimaging data points to modulated brain connectivity in patients. The genetic spontaneously hypertensive rat (SHR) model has been widely used to study pathophysiological underpinnings of ADHD and resting-state brain connectivity using functional magnetic resonance imaging. Here, functional ultrasound imaging, a new technique enabling fast measurement of cerebral blood volume (CBV), was used to further characterize resting-state functional connectivity - at both local and long-range - and visual response in SHR. We demonstrated that response to visual stimulation was increased in SHR in the visual cortex and the superior colliculus. They displayed altered long-range functional connectivity between spatially distinct regions. SHR also displayed modulated local connectivity, with strong increases of regional homogeneity in parts of the motor and visual cortex, along with decreases in the secondary cingulate cortex, the superior colliculus and the pretectal area. As CBV is intricately coupled to cerebral activity, these results suggest an abnormal neural activity in the SHR animal model, consistent with previous clinical studies and demonstrate the potential of functional ultrasound imaging as a translational tool in ADHD.

First‐Dose Methylphenidate‐Induced Changes in the Anti‐Saccade Task Performance and Outcome in Adults with Attention‐Deficit/Hyperactivity Disorder

Objective

We examined whether the anti‐saccade task (AST) performance after the first methylphenidate (MPH) dose could be associated with subsequent clinical outcome in adults with attention‐deficit/hyperactivity disorder (ADHD).

Methods

Ninety‐seven drug‐naive DSM‐5 ADHD adults participated in this study. The AST parameters were measured at baseline, after the first MPH‐dose (10 mg orally), and 6 months after chronic MPH treatment. Results were compared with those of 50 healthy control (HC) subjects.

Results

At baseline, ADHDs showed longer saccadic reaction times and more direction errors than HCs (both p < 0.00001). Acute and chronic MPH administration resulted in normalization of the AST performances. Multivariate regression analysis after adjusting for age, sex, weight, and severity of symptoms at baseline, revealed that a low percentage of direction errors after the first MPH‐dose (i.e., ≤10%) could predict remission at month 6 (OR: 5.84; 95% CI: 2.00–17.11; p = 0.001).

Conclusions

Our findings indicate that: (1) impairments of motor planning and response inhibition in adults with ADHD are improved with MPH, and (2) a low direction error percentage after the first MPH‐dose may be an independent predictor of remission.

ClinicalTrials.gov identifier: NCT03411434

The antisaccade task (AST) is useful to reveal impairments in inhibitory control in ADHD.

Never‐medicated adult ADHD subjects show delays in reaction times and increased direction errors.

Methyphenidate (MPH) administration, either acute or chronic, normalizes AST performances.

Direction error percentages after the first MPH‐dose could predict treatment outcome.

Organization of the inputs and outputs of the mouse superior colliculus

The superior colliculus (SC) receives diverse and robust cortical inputs to drive a range of cognitive and sensorimotor behaviors. However, it remains unclear how descending cortical input arising from higher-order associative areas coordinate with SC sensorimotor networks to influence its outputs. Here, we construct a comprehensive map of all cortico-tectal projections and identify four collicular zones with differential cortical inputs: medial (SC.m), centromedial (SC.cm), centrolateral (SC.cl) and lateral (SC.l). Further, we delineate the distinctive brain-wide input/output organization of each collicular zone, assemble multiple parallel cortico-tecto-thalamic subnetworks, and identify the somatotopic map in the SC that displays distinguishable spatial properties from the somatotopic maps in the neocortex and basal ganglia. Finally, we characterize interactions between those cortico-tecto-thalamic and cortico-basal ganglia-thalamic subnetworks. This study provides a structural basis for understanding how SC is involved in integrating different sensory modalities, translating sensory information to motor command, and coordinating different actions in goal-directed behaviors.

The relationship between sensory processing sensitivity and attention deficit hyperactivity disorder traits: A spectrum approach

The aim of the present study was to examine the relationship between sensory processing sensitivity (SPS) and symptoms of Attention Deficit Hyperactivity Disorder (ADHD) in adults. The Highly Sensitive Person Scale (HSPS) scale and the Adult ADHD Self-Report Scale (ASRS) were administered to a non-clinical group of 274 participants recruited from a university volunteers list. We found a highly significant positive correlation between number of self-reported ADHD traits and sensory sensitivity. Furthermore, ADHD traits and age were predictors of SPS and exploratory factor analysis revealed a factor that combined ADHD traits and items from the HSPS. The psychometric properties of the HSPS were also examined supporting the unidimensional nature of the concept. To our knowledge, this is the first study to identify a positive relationship between HSPS and ADHD traits in the general population. Our results further support recent findings suggesting abnormal sensory processing in ADHD.

Effect of a visual tracking intervention on attention and behavior of children with Attention Deficit Hyperactivity Disorder

Attention deficit hyperactivity disorder is characterized by several cognitive and behavioral problems such as inattention and impulsivity, abnormal control of eye movements and relocation, visual fixation and visuospatial perception. There is a link between core motor functions such as oculomotor function and cognition to the extent that the oculomotor system acts as a mediator between the motor and cognitive functions. Therefore, the effects of eye-tracking intervention were investigated on attention in these children. Thirty - nine boys with ADHD, 6 to 10 years of age were recruited and randomized to receive current occupational therapy (control group), or occupational therapy accompanied with eye-tracking exercises (experimental group). They were evaluated using the Conner's Parent Rating Scale, the Continuous Performance Task-2, and the Test of Visual-Motor Skills-Revised before and after the intervention. Significant improvements in the mean scores of cognitive problems (F=9/22), coping behavior (F=6.03) and hyperactivity (F=9.77) were detected in the posttest between the two groups (p<0.05). Furthermore, in the Continuous Performance Test scores, detectability (F=5.68), omission errors (F=17.89), commission errors (F=19.45), reaction time (F=8.95), variability (F=7.07), and preservation (F=6.33) showed significant differences between control and experimental groups (p<0.01). It appears that eye-tracking interventions designed based on the isolation of neck and eye movement might have an important role in improving cognitive function and coping behaviors in these children. It seems that these exercises could increase eye movement control; improve cognitive function and response inhibition.

The influence of subcortical shortcuts on disordered sensory and cognitive processing

The very earliest stages of sensory processing have the potential to alter how we perceive and respond to our environment. These initial processing circuits can incorporate subcortical regions, such as the thalamus and brainstem nuclei, which mediate complex interactions with the brain's cortical processing hierarchy. These subcortical pathways, many of which we share with other animals, are not merely vestigial but appear to function as 'shortcuts' that ensure processing efficiency and preservation of vital life-preserving functions, such as harm avoidance, adaptive social interactions and efficient decision-making. Here, we propose that functional interactions between these higher-order and lower-order brain areas contribute to atypical sensory and cognitive processing that characterizes numerous neuropsychiatric disorders.

Stereoacuity, Fusional Vergence Amplitudes, and Refractive Errors Prior to Treatment in Patients with Attention-Deficit Hyperactivity Disorder

Objectives:

To evaluate stereoacuity, fusional vergence amplitudes, and refractive errors in patients with attention-deficit hyperactivity disorder (ADHD).

Materials and Methods:

Twenty-three patients who were newly diagnosed as having ADHD and had not started medication, and 48 children without ADHD were included. Retrospective data analysis of comprehensive eye examination, stereoacuity, and fusional vergence amplitudes of the patients were performed.

Results:

The mean age at ADHD diagnosis was 10.68±2.34 (7-16) years in the ADHD group (14 male, 9 female) and 12.23±2.16 (7-15) years in the control group (25 male, 23 female) patients (p=0.605). The mean stereoacuity was 142.14±152.65 (15-480) sec/arc in patients with ADHD and 46.3±44.11 (15-240) sec/arc in the control group (p<0.001). For ADHD patients, the mean convergence and divergence amplitudes at distance were 19.87±8.40 (6 to 38) prism diopter (PD) and -9.09±-4.34 (-4 to -25) PD, and 37.30±12.81 (14 to 70) PD and -13.13±-3.45 (-4 to -20) PD at near, respectively. The mean cycloplegic spherical equivalent was 1.06±1.13 (-1 to 4.63) diopter in ADHD patients, with 6 patients having significant refractive errors (hyperopia in 4 patients, astigmatism in 2 patients). There were no significant differences between groups in terms of spherical equivalents (p=0.358) or convergence and divergence amplitudes at distance (p=0.289 and p=0.492, respectively) or near (p=0.452 and p=0.127, respectively).

Conclusion:

Fusional vergence amplitudes did not present significant difference, while the mean value of stereoacuity was significantly lower in newly diagnosed ADHD patients prior to treatment.

Enhancing the efficacy of 5-HT uptake inhibitors in the treatment of attention deficit hyperactivity disorder

Attention Deficit Hyperactivity Disorder (ADHD) is one of the most common childhood behavioural disorders, the frontline treatments for which are drugs with abuse potential. As a consequence, there is an urgent need to develop non addictive drug treatments with equivalent efficacy. Preclinical evidence suggests that selective serotonin uptake inhibitors (SSRIs) are likely to be effective in ADHD, however clinical reports suggest that SSRIs are of limited therapeutic value for the treatment of ADHD. We propose that this disconnect can be explained by the pattern of drug administration in existing clinical trials (administration for short periods of time, or intermittently) leading to inadequate control of the autoregulatory processes which control 5-HT release, most notably at the level of inhibitory 5-HT_1A somatodendritic autoreceptors. These autoreceptors reduce the firing rate of 5-HT neurons (limiting release) unless they are desensitised by a long term, frequent pattern of drug administration. As such, we argue that the participants in earlier trials were not administered SSRIs in a manner which realises any potential benefits of targeting 5-HT in the pharmacotherapy of ADHD. In light of this, we hypothesise that there may be under-researched potential to exploit 5-HT transmission therapeutically in ADHD, either through changing the administration regime, or by pharmacological means. Recent pharmacological research has successfully potentiated the effects of SSRIs in acute animal preparations by antagonising inhibitory 5-HT_1A autoreceptors prior to the administration of the SSRI fluoxetine. We suggest that combination therapies linking SSRIs and 5-HT_1A antagonists are a potential way forward in the development of efficacious non-addictive pharmacotherapies for ADHD.

Microsaccade rate as a measure of drug response

In 22 human subjects we measured microsaccade count across 60 brief fixation trials both pre- and post- administration of 300mg of caffeine. There was a statistically significant reduction in average microsaccade count post-caffeine administration, with a moderate effect size (Cohen's d of 0.42). Microsaccade count was stable within individuals across time points (Pearson's r of 0.89). Sensitivity analysis suggests that the pre/post caffeine effect size is robust to choice of parameters used to identify microsaccades. Bootstrap resampling suggests that both the pre/post-caffeine difference and the across-time stability within individuals could be reliably assessed with far fewer trials. The results support the use of microsaccade count as both a trait measure of individual differences and a state measure of caffeine response. We discuss the results in the context of the theory that the superior colliculus is central to the generation of microsaccades and hence that microsaccade rate may be a useful assay for at least some drug-induced changes at the level of the colliculus: a potentially useful tool in the development of therapies for disorders that may involve collicular dysfunction such as ADHD.

Sensory Over-Responsivity as an Added Dimension in ADHD

Years of research have added to our understanding of Attention Deficit Hyperactivity Disorder (ADHD). None-the-less there is still much that is poorly understood. There is a need for, and ongoing interest in, developing a deeper understanding of this disorder to optimally identify risk and better inform treatment. Here, we present a compilation of findings examining ADHD both behaviorally and using neurophysiologic markers. Drawing on early work of McIntosh and co-investigators, we examined response to sensory challenge in children with ADHD, measuring HPA activity and electrodermal response (EDR) secondary to sensory stressors. In addition, we have examined the relationship between these physiologic measures, and reports of behavioral sensory over-responsivity and anxiety. Findings suggest that sensory responsivity differentiates among children with ADHD and warrants consideration. We link these findings with research conducted both prior to and after our own work and emphasize that there a growing knowledge supporting a relationship between ADHD and sensory over-responsivity, but more research is needed. Given the call from the National Institute of Health to move toward a more dimensional diagnostic process for mental health concerns, and away from the more routine categorical diagnostic process, we suggest sensory over-responsivity as a dimension in the diagnostic process for children with ADHD.

Methylphenidate and alcohol effects on flash-evoked potentials, body temperature, and behavior in Long-Evans rats

Methylphenidate (MPD) is a psychostimulant used to treat attention deficit hyperactivity disorder (ADHD). Most adult ADHD patients use ethanol in combination with MPD. This research examined the effects of MPD and ethanol on flash-evoked potentials (FEPs; cortical responses frequently used to assess neural activity and sensory processing) recorded from the visual cortex (VC) and superior colliculus (SC; a structure involved in attention and orientation) of chronically implanted male Long-Evans rats, and on body temperature and open field behavior. For one group of rats, either saline or ethanol (2.0 g/kg) was given 5 min prior to either saline or MPD (2.9 mg/kg). FEPs were recorded 10 and 20 min later. In the VC, ethanol decreased amplitudes of several components, but increased P2. MPD increased N3, but decreased P3 and P4. Ethanol increased the latency of several components. In the SC, ethanol decreased all three components, while MPD increased P3. Ethanol increased latency of all components. During FEP testing, ethanol decreased body movement while MPD increased movement. In the open field, line crossings were increased but rearings were decreased by ethanol. Both ethanol and MPD produced hypothermia. A second group of rats was given MPD at 11.6 mg/kg. Ethanol decreased several VC amplitudes, but increased P2. MPD increased N3 amplitude but decreased amplitude for other components. MPD also counteracted the effect of ethanol on the amplitude of P2 and N3. Both ethanol and MPD increased the latency of several components. In the SC, ethanol decreased all component amplitudes, while MPD increased P3 but decreased N4. Ethanol increased all component latencies, while MPD increased latency for two components. During FEP testing, ethanol decreased body movement while MPD increased movement. In the open field, line crossings were increased by ethanol and MPD. Rearings were eliminated by ethanol in the open field but increased by MPD, and MPD counteracted the effect of ethanol on rearings. Both ethanol and MPD produced hypothermia. Some of these results might help explain why users take MPD and ethanol in combination in order to enable consuming larger amounts of alcohol.

Cognitive Control Over Visual Motion Processing - Are Children With ADHD Especially Compromised? A Pilot Study of Flanker Task Event-Related Potentials

Performance deficits and diminished brain activity during cognitive control and error processing are frequently reported in attention deficit/hyperactivity disorder (ADHD), indicating a “top-down” deficit in executive attention. So far, these findings are almost exclusively based on the processing of static visual forms, neglecting the importance of visual motion processing in everyday life as well as important attentional and neuroanatomical differences between processing static forms and visual motion. For the current study, we contrasted performance and electrophysiological parameters associated with cognitive control from two Flanker-Tasks using static stimuli and moving random dot patterns. Behavioral data and event-related potentials were recorded from 16 boys with ADHD (combined type) and 26 controls (aged 8–15 years). The ADHD group showed less accuracy especially for moving stimuli, and prolonged response times for both stimulus types. Analyses of electrophysiological parameters of cognitive control revealed trends for diminished N2-enhancements and smaller error-negativities (indicating medium effect sizes), and we detected significantly lower error positivities (large effect sizes) compared to controls, similarly for both static and moving stimuli. Taken together, the study supports evidence that motion processing is not fully developed in childhood and that the cognitive control deficit in ADHD is of higher order and independent of stimulus type.

A Low-Level Perceptual Correlate of Behavioral and Clinical Deficits in ADHD

In many studies of attention-deficit hyperactivity disorder (ADHD), stimulus encoding and processing (perceptual function) and response selection (executive function) have been intertwined. To dissociate deficits in these functions, we introduced a task that parametrically varied low-level stimulus features (orientation and color) for fine-grained analysis of perceptual function. It also required participants to switch their attention between feature dimensions on a trial-by-trial basis, thus taxing executive processes. Furthermore, we used a response paradigm that captured task-irrelevant motor output (TIMO), reflecting failures to use the correct stimulus-response rule. ADHD participants had substantially higher perceptual variability than controls, especially for orientation, as well as higher TIMO. In both ADHD and controls, TIMO was strongly affected by the switch manipulation. Across participants, the perceptual variability parameter was correlated with TIMO, suggesting that perceptual deficits are associated with executive function deficits. Based on perceptual variability alone, we were able to classify participants into ADHD and controls with a mean accuracy of about 77%. Participants' self-reported General Executive Composite score correlated not only with TIMO but also with the perceptual variability parameter. Our results highlight the role of perceptual deficits in ADHD and the usefulness of computational modeling of behavior in dissociating perceptual from executive processes.

The relationship between ADHD traits and sensory sensitivity in the general population

Preliminary studies in children and adults with Attention Deficit Hyperactivity Disorder (ADHD) report both hypo-responsiveness and hyper-responsiveness to sensory stimuli, as well as problems modulating sensory input. As it has been suggested that those with ADHD exist at the extreme end of a continuum of ADHD traits, which are also evident in the general population, we investigated the link between ADHD and sensory sensitivity in the general population. Two online questionnaires measuring ADHD traits and sensory responsivity across various sensory domains were administered to 234 participants. Results showed a highly significant positive correlation between the number of ADHD traits and the frequency of reported sensory processing problems. An increased number of sensory difficulties across all modalities were associated with the level of ADHD. Furthermore, ADHD traits predicted sensory difficulties and exploratory factor analysis revealed a factor that combined ADHD trait and sensory processing items. This is the first study to identify a positive relationship between sensory processing and ADHD traits in the general population. Our results suggest that sensory difficulties could be part of the ADHD phenotype.

Multisensory integration and ADHD-like traits: Evidence for an abnormal temporal integration window in ADHD

Abnormalities in multimodal processing have been found in many developmental disorders such as autism and dyslexia. However, surprisingly little empirical work has been conducted to test the integrity of multisensory integration in Attention Deficit Hyperactivity Disorder (ADHD). The main aim of the present study was to examine links between symptoms of ADHD (as measured using a self-report scale in a healthy adult population) and the temporal aspects of multisensory processing. More specifically, a Simultaneity Judgement (SJ) and a Temporal Order Judgement (TOJ) task were used in participants with low and high levels of ADHD-like traits to measure the temporal integration window and Just-Noticeable Difference (JND) (respectively) between the timing of an auditory beep and a visual pattern presented over a broad range of stimulus onset asynchronies. The Point of Subjective Similarity (PSS) was also measured in both cases. In the SJ task, participants with high levels of ADHD-like traits considered significantly fewer stimuli to be simultaneous than participants with high levels of ADHD-like traits, and the former were found to have significantly smaller temporal windows of integration (although no difference was found in the PSS in the SJ or TOJ tasks, or the JND in the latter). This is the first study to identify an abnormal temporal integration window in individuals with ADHD-like traits. Perceived temporal misalignment of two or more modalities can lead to distractibility (e.g., when the stimulus components from different modalities occur separated by too large of a temporal gap). Hence, an abnormality in the perception of simultaneity could lead to the increased distractibility seen in ADHD.

Effect of methylphenidate on visual responses in the superior colliculus in the anaesthetised rat: Role of cortical activation

The mechanism of action of psychostimulant drugs in the treatment of Attention Deficit Hyperactivity Disorder is still largely unknown, although recent evidence suggests one possibility is that the drugs affect the superior colliculus (SC). We have previously demonstrated that systemically administered d-amphetamine attenuates/abolishes visual responses to wholefield light flashes in the superficial layers of the SC in anaesthetised rats, and the present study sought to extend this work to methylphenidate (MPH). Anaesthetised rats were administered MPH at a range of doses (or saline) and subjected to monocular wholefield light flashes at two intensities, juxta-threshold and super-threshold. In contrast to d-amphetamine, systemic MPH produced an enhancement of visual activity at both intensities. Methylphenidate was also found to produce activation of the cortical EEG in anaesthetised rats. Furthermore, cortical activation induced by electrical stimulation of the pons was found to enhance visual responses in superficial layers of the SC, and when MPH was paired with pontine-induced cortical activation, the response-enhancing effects of MPH were substantially attenuated. Taken together, the results suggest that the enhancement of visual responses in the superficial layers of the SC by MPH in the anaesthetised rat is an artefact of the drug's interaction with cortical arousal.

Attention-Deficit Hyperactivity Disorder-Like Traits and Distractibility in the Visual Periphery

We examined the performance of nonclinical subjects with high and low levels of self-reported attention-deficit hyperactivity disorder (ADHD)-like traits in a novel distractibility paradigm with far peripheral visual distractors, the likely origin of many distractors in everyday life. Subjects were tested on a Sustained Attention to Response Task with distractors appearing before some of the target or nontarget stimuli. When the distractors appeared 80 ms before the targets or nontargets, participants with high levels of ADHD-like traits were less affected in their reaction times than those with lower levels. Reducing the distractor-target or nontarget interval to 10 ms removed the reaction time advantage for the high group. We suggest that at 80 ms, the distractors were cueing the arrival of the target or nontarget, and that those with high levels of ADHD-like traits were more sensitive to the cues. Increased sensitivity to stimuli in the visual periphery is consistent with hyperresponsiveness at the level of the superior colliculus.

Do children and adolescents with attention deficit hyperactivity disorder have ocular abnormalities?

PURPOSE

To investigate visual function and ocular features in children with attention deficit hyperactivity disorder (ADHD).

METHODS

Fifty-one children underwent a detailed ophthalmologic evaluation. Thirty-two were diagnosed with ADHD, and 19 children with attention deficit disorder (ADD). The mean age was 9.9±3.1 years.

RESULTS

The average best-corrected visual acuity of the better-seeing eye was 1 (range 0.9-1.25) and 0.96 (range 0.5-1.25) for the fellow eye. Eighteen percent (10) had amblyopia in one or both eyes (3 had strabismic and 7 had ametropic amblyopia). Heterotropia was found in 5 (10%), and absent stereo acuity was found in 3 (6%). Subnormal convergence amplitude was noted in 2 patients (4%). The mean spherical equivalent (SE) of the eyes in this study was 0.17±1.73 (range -5.5 to +7). Twenty-two subjects (43%) had a myopia of -0.50 D or higher. Hyperopia higher than 3.5 D was seen in 10 cases(20%), and astigmatism larger or equal to 1.0 D was observed in 10 patients (20%). With-the-rule a stigmatism was by far most common type in the 29 eyes with an astigmatic refractive error (59%).Significant ametropia was detected in 42 (83%) of the patients. In contrast to other studies, we did not find a higher rate of convergence insufficiency or heterotropia.

CONCLUSIONS

Children diagnosed with either ADHD or ADD can present with significant ametropia but infrequent heterotropia.

Prenatal and acute cocaine exposure affects neural responses and habituation to visual stimuli

Psychostimulants have many effects on visual function, from adverse following acute and prenatal exposure to therapeutic on attention deficit. To determine the impact of prenatal and acute cocaine exposure on visual processing, we studied neuronal responses to visual stimuli in two brain regions of a transgenic larval zebrafish expressing the calcium indicator GCaMP-HS. We found that both red light (LF) and dark (DF) flashes elicited similar responses in the optic tectum neuropil (TOn), while the dorsal telencephalon (dTe) responded only to LF. Acute cocaine (0.5 μM) reduced neuronal responses to LF in both brain regions but did not affect responses to DF. Repeated stimulus presentation (RSP) led to habituation of dTe neurons to LF. Acute cocaine prevented habituation. TOn habituated to DF, but not LF, and DF habituation was not modified by cocaine. Remarkably, prenatal cocaine exposure (PCE) prevented the effects of acute cocaine on LF response amplitude and habituation later in development in both brain regions, but did not affect DF responses. We discovered that, in spite of similar neural responses to LF and DF in the TO (superior colliculus in mammals), responses to LF are more complex, involving dTe (homologous to the cerebral cortex), and are more vulnerable to cocaine. Our results demonstrate that acute cocaine exposure affects visual processing differentially by brain region, and that PCE modifies zebrafish visual processing in multiple structures in a stimulus-dependent manner. These findings are in accordance with the major role that the optic tectum and cerebral cortex play in sustaining visual attention, and support the hypothesis that modification of these areas by PCE may be responsible for visual deficits noted in humans. This model offers new methodological approaches for studying the adverse and therapeutic effects of psychostimulants on attention, and for the development of new pharmacological interventions.

The influence of oculomotor tasks on postural control in dyslexic children

Dual task is known to affect postural stability in children. We explored the effect of visual tasks on postural control in thirty dyslexic children. A selected group of thirty chronological age-matched non-dyslexic children (mean age: 9.92 ± 0.35 years) and a group of thirty reading age-matched non-dyslexic children (mean reading age: 7.90 ± 0.25 years) were chosen for comparison. All children underwent ophthalmologic and optometric evaluation. Eye movements were recorded by a video-oculography system (EyeBrain® T2) and postural sway was recorded simultaneously by a force platform (TechnoConept®). All children performed fixations, pursuits, pro- and anti-saccades tasks. Dyslexic children showed significantly poor near fusional vergence ranges (convergence and divergence) with respect to the non-dyslexic children groups. During the postural task, quality of fixation and anti-saccade performance in dyslexic children were significantly worse compared to the two non-dyslexic children groups. In contrast, the number of catch-up saccades during pursuits and the latency of pro- and anti-saccades were similar in the three groups of children examined. Concerning postural quality, dyslexic children were more unstable than chronological age-matched non-dyslexic children group. For all three groups of children tested we also observed that executing saccades (pro- and anti-saccades) reduced postural values significantly in comparison with fixation and pursuit tasks. The impairment in convergence and divergence fusional capabilities could be due to an immaturity in cortical structures controlling the vergence system. The poor oculomotor performance reported in dyslexic children suggested a deficit in allocating visual attention and their postural instability observed is in line with the cerebellar impairment previously reported in dyslexic children. Finally, pro- or anti-saccades reduce postural values compared to fixation and pursuit tasks in all groups of children tested, suggesting a different influence of visual tasks on postural control according to their attentional demand.

Enhanced visual responses in the superior colliculus in an animal model of attention-deficit hyperactivity disorder and their suppression by D-amphetamine

Attention-deficit hyperactivity disorder (ADHD) is a prevalent neurodevelopmental disorder characterized by overactivity, impulsiveness and attentional problems, including an increase in distractibility. A structure that is intimately linked with distractibility is the superior colliculus (SC), a midbrain sensory structure which plays a particular role in the production of eye and head movements. Although others have proposed the involvement of such diverse elements as the frontal cortex and forebrain noradrenaline in ADHD, given the role of the colliculus in distractibility and the increased distractibility in ADHD, we have proposed that distractibility in ADHD arises due to collicular sensory hyper-responsiveness. To further investigate this possibility, we recorded the extracellular activity (multi-unit (MUA) and local field potential (LFP)) in the superficial visual layers of the SC in an animal model of ADHD, the New Zealand genetically hypertensive (GH) rat, in response to wholefield light flashes. The MUA and LFP peak amplitude and summed activity within a one-second time window post-stimulus were both significantly greater in GH rats than in Wistar controls, across the full range of stimulus intensities. Given that baseline firing rate did not differ between the strains, this suggests that the signal-to-noise ratio is elevated in GH animals. D-Amphetamine reduced the peak amplitude and summed activity of the multi-unit response in Wistar animals. It also reduced the peak amplitude and summed activity of the multi-unit response in GH animals, at higher doses bringing it down to levels that were equivalent to those of Wistar animals at baseline. The present results provide convergent evidence that a collicular dysfunction (sensory hyper-responsiveness) is present in ADHD, and that it may underlie the enhanced distractibility. In addition, D-amphetamine - a widely used treatment in ADHD - may have one of its loci of therapeutic action at the level of the colliculus.

Defective response inhibition and collicular noradrenaline enrichment in mice with duplicated retinotopic map in the superior colliculus

The superior colliculus is a hub for multisensory integration necessary for visuo-spatial orientation, control of gaze movements and attention. The multiple functions of the superior colliculus have prompted hypotheses about its involvement in neuropsychiatric conditions, but to date, this topic has not been addressed experimentally. We describe experiments on genetically modified mice, the Isl2-EphA3 knock-in line, that show a well-characterized duplication of the retino-collicular and cortico-collicular axonal projections leading to hyperstimulation of the superior colliculus. To explore the functional impact of collicular hyperstimulation, we compared the performance of homozygous knock-in, heterozygous knock-in and wild-type mice in several behavioral tasks requiring collicular activity. The light/dark box test and Go/No-Go conditioning task revealed that homozygous mutant mice exhibit defective response inhibition, a form of impulsivity. This defect was specific to attention as other tests showed no differences in visually driven behavior, motivation, visuo-spatial learning and sensorimotor abilities among the different groups of mice. Monoamine quantification and gene expression profiling demonstrated a specific enrichment of noradrenaline only in the superficial layers of the superior colliculus of Isl2-EphA3 knock-in mice, where the retinotopy is duplicated, whereas transcript levels of receptors, transporters and metabolic enzymes of the monoaminergic pathway were not affected. We demonstrate that the defect in response inhibition is a consequence of noradrenaline imbalance in the superficial layers of the superior colliculus caused by retinotopic map duplication. Our results suggest that structural abnormalities in the superior colliculus can cause defective response inhibition, a key feature of attention-deficit disorders.

Subsite awareness in neuropathology evaluation of National Toxicology Program (NTP) studies: a review of select neuroanatomical structures with their functional significance in rodents

This review article is designed to serve as an introductory guide in neuroanatomy for toxicologic pathologists evaluating general toxicity studies. The article provides an overview of approximately 50 neuroanatomical subsites and their functional significance across 7 transverse sections of the brain. Also reviewed are 3 sections of the spinal cord, cranial and peripheral nerves (trigeminal and sciatic, respectively), and intestinal autonomic ganglia. The review is limited to the evaluation of hematoxylin and eosin-stained tissue sections, as light microscopic evaluation of these sections is an integral part of the first-tier toxicity screening of environmental chemicals, drugs, and other agents. Prominent neuroanatomical sites associated with major neurological disorders are noted. This guide, when used in conjunction with detailed neuroanatomic atlases, may aid in an understanding of the significance of functional neuroanatomy, thereby improving the characterization of neurotoxicity in general toxicity and safety evaluation studies.

Saccadic alterations in severe developmental dyslexia

It is not sure if persons with dyslexia have ocular motor deficits in addition to their deficits in rapid visual information processing. A 15-year-old boy afflicted by severe dyslexia was submitted to saccadic eye movement recording. Neurological and ophthalmic examinations were normal apart from the presence of an esophoria for near and slightly longer latencies of pattern visual evoked potentials. Subclinical saccadic alterations were present, which could be at the basis of the reading pathology: (1) low velocities (and larger durations) of the adducting saccades of the left eye with undershooting and long-lasting postsaccadic onward drift, typical of the internuclear ophthalmoplegia; (2) saccades interrupted in mid-flight and fixation instability, which are present in cases of brainstem premotor disturbances.

Saccadic eye movement applications for psychiatric disorders

OBJECTIVE

The study presented here analyzed the patterns of relationship between oculomotor performance and psychopathology, focusing on depression, bipolar disorder, schizophrenia, attention-deficit hyperactivity disorder, and anxiety disorder.

METHODS

Scientific articles published from 1967 to 2013 in the PubMed/Medline, ISI Web of Knowledge, Cochrane, and SciELO databases were reviewed.

RESULTS

Saccadic eye movement appears to be heavily involved in psychiatric diseases covered in this review via a direct mechanism. The changes seen in the execution of eye movement tasks in patients with psychopathologies of various studies confirm that eye movement is associated with the cognitive and motor system.

CONCLUSION

Saccadic eye movement changes appear to be heavily involved in the psychiatric disorders covered in this review and may be considered a possible marker of some disorders. The few existing studies that approach the topic demonstrate a need to improve the experimental paradigms, as well as the methods of analysis. Most of them report behavioral variables (latency/reaction time), though electrophysiological measures are absent.

Abnormal air righting behaviour in the spontaneously hypertensive rat model of ADHD

The spontaneously hypertensive rat (SHR) is the most commonly used model of attention-deficit hyperactivity disorder (ADHD), displaying the main symptoms of the disorder which are responsive to psychostimulant treatments. Research to date has focused on behavioural tests investigating functioning of the striatum or prefrontal cortex in these rats. However, there is now evidence that the superior colliculus, a structure associated with head and eye movements, may also be dysfunctional in ADHD. Therefore, the aim of this study was to investigate whether the SHR demonstrated impairment in collicular-dependent behaviour. To this end, we examined air righting behaviour, which has previously been shown to be modulated in a height-dependent manner reliant on a functional superior colliculus. We assessed SHR, Wistar Kyotos and Wistars on static righting and air righting at 50 and 10 cm drop heights. There were no differences in static righting, indicating that there were no gross motor differences that would confound air righting. Qualitative analysis of video footage of the righting did not reveal any changes previously associated with collicular damage, unique to the SHR. However, the SHR did show impairment in height-dependent modulation of righting in contrast to both control strains, such that the SHR failed to modulate righting latency according to drop height. This failure is indicative of collicular abnormality. Given that many rodent tests of attentional mechanisms involve head and eye orienting, which are heavily dependent on the colliculus, a collicular dysfunction has strong implications for the type of attentional task used in this strain.

Drug therapies for attentional disorders alter the signal-to-noise ratio in the superior colliculus

Despite high levels of use, the mechanism of action of effective pharmacotherapies in attention deficit hyperactivity disorder (ADHD) is unknown. It has recently been hypothesized that one site of therapeutic action is the midbrain superior colliculus, a structure traditionally associated with visual processing, but also strongly implicated in distractibility, a core symptom of ADHD. We used male juvenile Wistar rats to examine the effects of therapeutically relevant doses of methylphenidate and d-amphetamine on collicular activity in vitro. Here we report a novel shared mechanism of the two drugs whereby they enhance the signal-to-noise ratio in the superior colliculus. The effects on the signal-to-noise ratio were mediated by serotonin (5-HT) via a pre-synaptic mechanism. This modulatory action would bias the system towards salient events and lead to an overall decrease in distractibility.