Sources of auditory selective attention and the effects of methylphenidate in children with attention-deficit/hyperactivity disorder

Effects of Methylphenidate on Reaction Time in Children with Attention Deficit / Hyperactivity Disorder

INTRODUCTION

Attention-deficit/hyperactivity disorder (ADHD) is associated with a broad range of neuropsychological impairments that are attenuated with methylphenidate (MPH) treatment. The aim of this study was to determine how MPH effects attentional functioning in terms of reaction time (RT) in ADHD.

METHODS

Eighteen pre-medicated ADHD children (7 to 12 years old) and eighteen gender matched normal controls (7 to 12 years old) were included in the study. Participants performed an auditory attention task and the RT of participants to each target response was calculated automatically. The same test was repeated 3 months after OROS-MPH administration for ADHD group. RT, RT standard deviation (RTSD), and response errors (omission and commission errors) were compared between control and pre-MPH ADHD groups, and between Pre-MPH and post-MPH ADHD groups.

RESULTS

Relative to control subjects, significantly longer RTs, higher RTSD and more errors of omission were observed in unmedicated ADHD children during auditory attention task. Analyses revealed significant effects of medication across all measures except commission errors. After treatment RTs were faster, RTSD values were lower, and errors of omission were attenuated compared to pre-medication condition in ADHD group. There were no significant differences in terms of commission errors between groups.

CONCLUSION

In this study it was observed that MPH reduced RTs to stimuli, attenuated omission errors during the task in ADHD group and after 3 months of treatment ADHD children showed similar patterns in RT as compared to controls. Results suggest that when treating ADHD, it might help clinicians to evaluate objective and non-invasive cognitive outcomes such as RT, RTSD and response errors to evaluate the effects of treatment.

A comparison of social cognitive profiles in children with autism spectrum disorders and attention-deficit/hyperactivity disorder: a matter of quantitative but not qualitative difference?

The aim of this study was to compare social cognitive profiles of children and adolescents with Autism Spectrum Disorders (ASD) and ADHD. Participants diagnosed with an ASD (n = 137) were compared to participants with ADHD (n = 436) on tests of facial and vocal affect recognition, social judgment and problem-solving, and parent- and teacher-report of social functioning. Both groups performed significantly worse than the normative sample on all measures. Although the ASD group had more severe deficits, the pattern of deficits was surprisingly similar between groups, suggesting that social cognitive deficit patterns may be more similar in ASD and ADHD than previously thought. Thus, like those with ASDs, individuals with ADHD may also need to be routinely considered for treatments targeting social skills.

The effects of methylphenidate on cognitive function in children with attention-deficit/hyperactivity disorder

Focusing on behavioral criteria for attention-deficit/hyperactivity disorder (ADHD) diagnosis leads to considerable neuropsychological profile heterogeneity among diagnosed children, as well as variable response to methylphenidate (MPH) treatment. Documenting "cold" executive working memory (EWM) or "hot" self-regulation (SR) neuropsychological impairments could aid in the differential diagnosis of ADHD subtypes and may help to determine the optimal MPH treatment dose. In this study, children with ADHD inattentive type (n = 19), combined type (n = 33), and hyperactive-impulse type (n = 4) underwent randomized controlled MPH trials; neuropsychological, behavioral, and observational data were collected to evaluate the children's responses. Those with moderate or significant baseline EWM/SR impairment showed robust MPH response, whereas response for those with lower baseline impairment was equivocal. Implications for medication use and titration, academic achievement, and long-term treatment efficacy are examined.

Executive impairment determines ADHD medication response: implications for academic achievement

Methylphenidate (MPH) often ameliorates attention-deficit/hyperactivity disorder (ADHD) behavioral dysfunction according to indirect informant reports and rating scales. The standard of care behavioral MPH titration approach seldom includes direct neuropsychological or academic assessment data to determine treatment efficacy. Documenting "cool" executive-working memory (EWM) and "hot" self-regulation (SR) neuropsychological impairments could aid in differential diagnosis of ADHD subtypes and determining cognitive and academic MPH response. In this study, children aged 6 to 16 with ADHD inattentive type (IT; n = 19) and combined type (n = 33)/hyperactive-impulsive type (n = 4) (CT) participated in double-blind placebo-controlled MPH trials with baseline and randomized placebo, low MPH dose, and high MPH dose conditions. EWM/ SR measures and behavior ratings/classroom observations were rank ordered separately across conditions, with nonparametric randomization tests conducted to determine individual MPH response. Participants were subsequently grouped according to their level of cool EWM and hot SR circuit dysfunction. Robust cognitive and behavioral MPH response was achieved for children with significant baseline EWM/SR impairment, yet response was poor for those with adequate EWM/ SR baseline performance. Even for strong MPH responders, the best dose for neuropsychological functioning was typically lower than the best dose for behavior. Findings offer one possible explanation for why long-term academic MPH treatment gains in ADHD have not been realized. Implications for academic achievement and medication titration practices for children with behaviorally diagnosed ADHD will be discussed.

How human electrophysiology informs psychopharmacology: from bottom-up driven processing to top-down control

This review surveys human event-related brain potential (ERP) and event-related magnetic field (ERF) approaches to psychopharmacology and psychopathology, and the way in which they complement behavioral studies and other neuroimaging modalities. The major paradigms involving ERP/ERF are P50 suppression, loudness-dependent auditory evoked potential (LDAEP), mismatch negativity (MMN), P300, mental chronometry, inhibitory control, and conflict processing (eg, error-related negativity (ERN)). Together these paradigms cover a range of more bottom-up driven to more top-down controlled processes. A number of relationships between the major neurotransmitter systems and electrocortical mechanisms are highlighted. These include the role of dopamine in conflict processing, and perceptual processing vs motor preparation; the role of serotonin in P50 suppression, LDAEP, and MMN; glutamate/NMDA and MMN; and the role of acetylcholine in P300 generation and memory-related processes. A preliminary taxonomy for these relationships is provided, which should be helpful in attuning possible new treatments or new applications of existing treatments to various disorders.

Impaired attentional modulation of auditory evoked potentials in N-methyl-D-aspartate NR1 hypomorphic mice

In human neurophysiology, auditory event-related potentials (AEPs) are used to investigate cognitive processes such as selective attention. Selective attention to specific tones causes a negative enhancement of AEPs known as processing negativity (PN), which is reduced in patients with schizophrenia. The evidence suggests that impaired selective attention in these patients may partially depend on deficient N-methyl-D-aspartate receptor (NMDAR)-mediated signaling. The goal of this study was to corroborate the involvement of the NMDAR in selective attention using a mouse model. To this end, we first investigated the presence of PN-like activity in C57BL/6J mice by recording AEPs during a fear-conditioning paradigm. Two alternating trains of tones, differing in stimulus duration, were presented on 7 subsequent days. One group received a mild foot shock delivered within the presentation of one train (conditioning train) on days 3-5 (conditioning days), while controls were never shocked. The fear-conditioned group (n= 9) indeed showed a PN-like activity during conditioning days manifested as a significant positive enhancement in the AEPs to the stimuli in the conditioning train that was not observed in the controls. The same paradigm was then applied to mice with reduced expression of the NMDAR1 (NR1) subunit and to a wild-type control group (each group n= 6). The NR1 mutants showed an associative AEP enhancement, but its magnitude was significantly reduced as compared with the magnitude in wild-type mice. We conclude that electrophysiological manifestations of selective attention are observable yet of different polarity in mice and that they require intact NMDAR-mediated signaling. Thus, deficient NMDAR functioning may contribute to abnormal selective attention in schizophrenia.

Chronic methylphenidate modulates locomotor activity and sensory evoked responses in the VTA and NAc of freely behaving rats

Repeated exposure to psychostimulants leads to behavioral sensitization. The mode of action of brain circuitry responsible for behavioral sensitization is not well understood. There is some evidence that psychostimulants, such as amphetamine and cocaine, activate the ventral tegmental area (VTA) and nucleus accumbens (NAc). However, little is known about the effect of methylphenidate (MPD) on the electrophysiological properties of VTA and NAc neurons. The study was designed to investigate the chronic effects of MPD administration on sensory evoked field potentials of VTA and NAc in freely behaving rats previously implanted with permanent electrodes. On experimental day 1, locomotor behavior was recorded for 2 h post-saline injection followed by sensory evoked field potential recordings after saline and three different escalating (0.6, 2.5, and 10.0 mg/kg) MPD doses. After completion of the last recording, the rat was returned to its home cage. To induce behavioral sensitization, animals were injected for five days with 2.5 mg/kg MPD. Following a rechallenge with saline and identical MPD doses as those given on experimental day 1, locomotor recording of the rat was also performed on experimental days 2, 6 and 11. Results showed that repeated administration of MPD increased locomotion in dose-response manner and elicited behavioral sensitization, while the amplitude of the sensory evoked field responses of the VTA and NAc exhibited dose-response attenuation on both recording days (days 1 and 10). In addition, repeated administration of MPD resulted in attenuating the baseline amplitudes of sensory input on experimental day 10, while MPD administration on experimental day 10 elicited further attenuation of the VTA and NAc sensory evoked responses. Such further attenuation can be interpreted as electrophysiological sensitization.

Methylphenidate enhances noradrenergic transmission and suppresses mid- and long-latency sensory responses in the primary somatosensory cortex of awake rats

Noradrenergic neurons send widespread projections to sensory networks throughout the brain and regulate sensory processing via norepinephrine (NE) release. As a catecholamine reuptake blocker, methylphenidate (MPH) is likely to interact with noradrenergic transmission and NE modulatory action on sensory systems. To characterize the neurochemical actions of MPH in the primary sensory cortex of freely behaving rats and their consequences on sensory processing, we measured extracellular NE levels in the primary somatosensory (SI) cortex by microdialysis and recorded basal and sensory-evoked discharge of infragranular SI cortical neurons, before and after intraperitoneal administrations of saline or MPH (1 and 5 mg/kg). Both doses of MPH significantly increased NE levels in the SI cortex (+64 and +101%, respectively). In most neurons, stimulation of the whisker-pad induced a triphasic response, consisting of a short-latency excitation [4.7 +/- 0.2 (SE) ms] followed by a postexcitatory inhibition (36 +/- 1.5 ms) and a long-latency excitation (105 +/- 2.6 ms). Under control conditions, the behavioral state of the animal was correlated with the magnitude of the short-latency excitation but not with other aspects of the basal and sensory-evoked discharge of SI cortical neurons. At 5 mg/kg, MPH significantly increased locomotor activity and induced a significant suppression of the short-latency excitation, which probably resulted from the MPH-induced change in behavior. In addition, both doses of MPH suppressed the postexcitatory inhibition and the long-latency excitation evoked by the stimulation of the whisker pad. These effects did not seem to result from the locomotor effect of MPH and probably involved MPH-induced enhancement of noradrenergic transmission.

The effects of auditory attention measured from human electrocorticograms

OBJECTIVE

A central question in auditory electrophysiology has been whether selective attention can modulate exogenous components of the scalp-recorded N1 (the 'N1 effect'). Intracranial electrocorticograms were used in the current work to investigate this issue in greater anatomical detail.

METHODS

Data were recorded from subdural electrodes placed across temporal cortex in 6 patient-volunteers undergoing diagnostic procedures for medically intractable epilepsy. Patients performed a dichotic listening task in which they alternately attended to a series of tones presented to both ears (mean ISI 800 ms) by responding to rare frequency deviants.

RESULTS

Effects of attention were measured on the largest negative and positive waveform deflections observed between 70 and 220 ms post-stimulus for stimuli presented contralateral to grid location. Peak deflections were most often recorded from the upper bank of the posterior superior temporal gyrus at approximately 89 and 173 ms on average (labeled N90stg and P170stg, respectively). Selective attention had little effect on peak latencies but significantly increased the N90stg for 3 subjects, increased the P170stg for two subjects, and decreased the P170stg for two other subjects.

CONCLUSIONS

Selective auditory attention can modulate neural response in auditory cortex.

SIGNIFICANCE

The effects of attention on the scalp-recorded N1 component may arise in part from the enhancement of exogenous responses in temporal cortex.

Sensory-evoked potentials recordings from the ventral tegmental area, nucleus accumbens, prefrontal cortex, and caudate nucleus and locomotor activity are modulated in dose–response characteristics by methylphenidate

Most of the studies investigating the effects of methylphenidate (MPD) are using behavioral and biochemical approaches. There are some electrophysiological studies about the effects of MPD on spontaneous electrical activity; however, there is none about the effects of MPD on sensory inputs. The objectives of the present study were to investigate the MPD dose-response characteristics on locomotor activity and sensory inputs using acoustic stimuli. Freely behaving rats previously implanted with semi-microelectrodes were used to record from four brain areas known to be sites of psychostimulant action. For locomotor behavior assessment, rats received saline on experimental day 1 and an acute administration of MPD (0.6, 2.5, or 10.0 mg/kg, i.p.) on experimental day 2. Using an automated, computerized activity-monitoring system, locomotor behavior was recorded for 2-h postinjection on both days. For the electrophysiological experiments, animals were implanted with permanent electrodes in the ventral tegmental area (VTA), nucleus accumbens (NAc), prefrontal cortex (PFC), and caudate nucleus (CN) under general anesthesia. Five to seven days after electrode implantation, they were used to study the effects of three different MPD doses on the response to sensory inputs. The lowest dose of MPD (0.6 mg/kg, i.p.) failed to alter locomotor activity, while the two higher MPD doses (2.5 and 10.0 mg/kg) elicited increase in locomotion, with the 10.0 mg/kg dose increased at least twice as much as the 2.5 mg/kg dose. However, the same three MPD doses elicited significant attenuation of sensory inputs in dose-response characteristics, i.e., as MPD dose increased, evoked sensory inputs decreased. These opposite effects (motor activation and sensory input suppression) were further discussed.

Maturation processes in automatic change detection as revealed by event-related brain potentials and dipole source localization: significance for adult AD/HD

Mismatch negativity (MMN) is an event-related potential reflecting automatic attention-related information processing marking the detection of auditory change. The bilateral scalp distribution develops by 14 years of age, and is elicited with adult latencies by 17 years. But consistent with reports of continued brain maturation after adolescence, we show here that features of the temporal and frontal lobe dipole sources also continue to develop in the third decade of life. This has consequences for studies of the developmental course of MMN anomalies, from childhood into adulthood, in attention-deficit/hyperactivity disorder. Two groups of healthy subjects with mean ages of 17 and 30 years were presented with a 3-tone auditory oddball. The duration-deviant MMN was recorded during attention to a visual discrimination (auditory-passive condition) and an active auditory discrimination. MMN amplitudes were smaller in the older subjects and the MMN lasted longer over the right hemisphere. Latencies and moments of the four dipoles in the temporal and frontal lobes did not distinguish the two subject-groups. But both temporal lobe sources were located significantly more ventrally and further left in the young adult than in the adolescent subjects. The left cingular source moved posteriorly and the right inferior frontal source moved antero-medially in the older subjects. Brain development in the third decade may cause the two frontal sources to move apart on the rostro-caudal axis but the temporal lobe sources to move left on the lateral and down on the dorsoventral axes. Thus special care is necessary in interpreting putative dysfunctional neurobiological changes in developmental attention-deficit disorders where as-yet-unspecified sub-groups may show a late developmental lag, partial lag, or no lag at all, associated with other impairments.

Attention deficit and impulsivity: Selecting, shifting, and stopping

The present selective review addresses attention, inhibition, and their underlying brain mechanisms, especially in relation to attention deficit/hyperactivity disorders (AD/HD), and the effects of methylphenidate. In particular, event-related potential (ERP) studies suggest a deficit in the early-filtering aspect of selective attention in children with AD/HD. Results from stop tasks are consistent with impairments in stopping performance in AD/HD, but in children (as opposed to adults) these effects cannot be easily dissociated from more general impairments in attention to the task, and therefore an interpretation in terms of inhibitory control is not straightforward. On the other hand, the beneficial effects of methylphenidate are more specific to stopping, and there are no clearcut effects of methylphenidate on measures of selective attention. Even when group differences pertain specifically to stopping performance (as with adults with AD/HD), ERP evidence suggests at least a partial contribution of differences in switching attention to the stop signal, as revealed in measures of sensory cortex activation. ERP evidence from cued go/nogo tasks underlines the importance of taking into account the contribution of higher order control processes involved in anticipation of and preparation for task stimuli. It suggests that in certain conditions, expectancy, rather than response bias, contributes to increased behavioral response tendencies, and that a presumed index of response inhibition, the nogo N2, may rather reflect conflict monitoring. In sum, direct reflections of brain activity suggest that mechanisms of expectation and attention, rather than of response bias or inhibitory control, govern behavioral manifestations of impulsivity.