Dopamine modulates attentional control of auditory perception: DARPP-32 (PPP1R1B) genotype effects on behavior and cortical evoked potentials

Cortical processes of multisensory plausibility modulation of vibrotactile perception in virtual environments in middled-aged and older adults

Digital technologies, such as virtual or augmented reality, can potentially support neurocognitive functions of the aging populations worldwide and complement existing intervention methods. However, aging-related declines in the frontal-parietal network and dopaminergic modulation which progress gradually across the later periods of the adult lifespan may affect the processing of multisensory congruence and expectancy based contextual plausibility. We assessed hemodynamic brain responses while middle-aged and old adults experienced car-riding virtual-reality scenarios where the plausibility of vibrotactile stimulations was manipulated by delivering stimulus intensities that were either congruent or incongruent with the digitalized audio-visual contexts of the respective scenarios. Relative to previous findings observed in young adults, although highly plausible vibrotactile stimulations confirming with contextual expectations also elicited higher brain hemodynamic responses in middle-aged and old adults, this effect was limited to virtual scenarios with extreme expectancy violations. Moreover, individual differences in plausibility-related frontal activity did not correlate with plausibility violation costs in the sensorimotor cortex, indicating less systematic frontal context-based sensory filtering in older ages. These findings have practical implications for advancing digital technologies to support aging societies.

The effect of methylphenidate on pain perception thresholds in children with attention deficit hyperactivity disorder

BACKGROUND

Pain perception is important in children with attention deficit hyperactivity disorder (ADHD) since they are more likely to experience painful events due to increased accident rates. The aim of this study is to contribute to the literature concerning the relationship between ADHD diagnosis, methylphenidate (MPH) therapy, and pain thresholds, since findings regarding the change in pain perception in children with ADHD are scarce and inconsistent.

METHODS

Children aged 8-13 years constituted both the ADHD group (n = 82) and the healthy controls (n = 41). The ADHD group was divided into two subgroups, ADHD without MPH (not treated pharmacologically) and ADHD with MPH (treated pharmacologically for at least three-months). The Conners' Parent Rating Scale-Revised: Short Form was employed to assess ADHD, a visual analog scale was applied to evaluate chronic pain severity, and a manual pressure algometer was used to assess pain thresholds.

RESULT

Children with ADHD had lower pain thresholds than the healthy controls (P < 0.05). However, lower regional pain thresholds were observed in the ADHD group without MPH compared to both the healthy control and ADHD with MPH groups. Although pain thresholds in the ADHD with MPH group were regionally lower than in the healthy controls, low pain thresholds were found in fewer regions compared to the ADHD without MPH group.

CONCLUSIONS

Children with ADHD are more sensitive to pain sensation, and MPH may help normalize these individuals' pain experiences by raising pain thresholds. Families and clinicians must be aware of situations that may cause pain in children with ADHD. In addition, these children's low threshold for pain may lead them to experience it more intensely.

Digitally embodied lifespan neurocognitive development and Tactile Internet: Transdisciplinary challenges and opportunities

Mechanisms underlying perceptual processing and inference undergo substantial changes across the lifespan. If utilized properly, technologies could support and buffer the relatively more limited neurocognitive functions in the still developing or aging brains. Over the past decade, a new type of digital communication infrastructure, known as the "Tactile Internet (TI)," is emerging in the fields of telecommunication, sensor and actuator technologies and machine learning. A key aim of the TI is to enable humans to experience and interact with remote and virtual environments through digitalized multimodal sensory signals that also include the haptic (tactile and kinesthetic) sense. Besides their applied focus, such technologies may offer new opportunities for the research tapping into mechanisms of digitally embodied perception and cognition as well as how they may differ across age cohorts. However, there are challenges in translating empirical findings and theories about neurocognitive mechanisms of perception and lifespan development into the day-to-day practices of engineering research and technological development. On the one hand, the capacity and efficiency of digital communication are affected by signal transmission noise according to Shannon's (1949) Information Theory. On the other hand, neurotransmitters, which have been postulated as means that regulate the signal-to-noise ratio of neural information processing (e.g., Servan-Schreiber et al., 1990), decline substantially during aging. Thus, here we highlight neuronal gain control of perceptual processing and perceptual inference to illustrate potential interfaces for developing age-adjusted technologies to enable plausible multisensory digital embodiments for perceptual and cognitive interactions in remote or virtual environments.

Anodal transcranial direct current stimulation enhances the efficiency of functional brain network communication during auditory attentional control

Attentional control is crucial for selectively attending to relevant information when our brain is confronted with a multitude of sensory signals. Graph-theoretical measures provide a powerful tool for investigating the efficiency of brain network communication in separating and integrating information. Albeit, it has been demonstrated that anodal transcranial direct current stimulation (atDCS) can boost auditory attention in situations with high control demands, its effect on neurophysiological mechanisms of functional brain network communication in situations when attentional focus conflicts with perceptual saliency remain unclear. This study investigated the effects of atDCS on network connectivity and θ-oscillatory power under different levels of attentional-perceptual conflict. We hypothesized that the benefit of atDCS on network communication efficiency would be particularly apparent in conditions requiring high attentional control. Thirty young adults participated in a dichotic listening task with intensity manipulation, while EEG activity was recorded. In a cross-over design, participants underwent right frontal atDCS and sham stimulations in two separate sessions. Time-frequency decomposition and graph-theoretical analyses of network efficiency (using "small-world" properties) were used to quantify θ-oscillatory power and brain network efficiency, respectively. The atDCS-induced effect on task efficiency in the most demanding condition was mirrored only by an increase in network efficiency during atDCS compared with the sham stimulation. These findings are corroborated by Bayesian analyses. AtDCS-induced performance enhancement under high levels of attentional-perceptual conflicts is accompanied by an increase in network efficiency. Graph-theoretical measures can serve as a metric to quantify the effects of noninvasive brain stimulation on the separation and integration of information in the brain.NEW & NOTEWORTHY As compared with sham stimulation, application of atDCS enhances θ-oscillation-based network efficiency, but it has no impact on θ-oscillation power. Individual differences in θ-oscillation-based network efficiency correlated with performance efficiency under the sham stimulation.

Plasma levels of dopamine metabolite correlate with mismatch negativity in patients with schizophrenia

AIM

Mismatch negativity (MMN) deficit is one of the most robust and replicable findings in schizophrenia, and primarily reflects deficient functioning of the N-methyl-D-aspartate (NMDA) receptor system. Although the dopamine receptor is known not to modulate MMN over the short term, it is unclear whether the dopamine system affects MMN in the long term.

METHODS

We explored correlations between MMN and levels of plasma dopamine and serotonin metabolites in 18 patients with schizophrenia psychiatrically evaluated with the Positive and Negative Syndrome Scale (PANSS).

RESULTS

A significant negative correlation exists between MMN amplitude and plasma levels of dopamine metabolites. Plasma serotonin metabolite levels were not correlated with MMN. The PANSS total score and Negative score also showed negative correlations with MMN amplitude.

CONCLUSION

The usual strong therapeutic blockade of dopamine receptors applied in cases of schizophrenia may reduce MMN over the long term.

The system-neurophysiological basis for how methylphenidate modulates perceptual-attentional conflicts during auditory processing

The ability to selectively perceive and flexibly attend to relevant sensory signals in the environment is essential for action control. Whereas neuromodulation of sensory or attentional processing is often investigated, neuromodulation of interactive effects between perception and attention, that is, high attentional control demand when the relevant sensory information is perceptually less salient than the irrelevant one, is not well understood. To fill this gap, this pharmacological-electroencephalogram (EEG) study applied an intensity-modulated, focused-attention dichotic listening paradigm together with temporal EEG signal decomposition and source localization analyses. We used a double-blind MPH/placebo crossover design to delineate the effects of methylphenidate (MPH)-a dopamine/norepinephrine transporter blocker-on the resolution of perceptual-attentional conflicts, when perceptual saliency and attentional focus favor opposing ears, in healthy young adults. We show that MPH increased behavioral performance specifically in the condition with the most pronounced conflict between perceptual saliency and attentional focus. On the neurophysiological level, MPH effects in line with the behavioral data were observed after accounting for intraindividual variability in the signal. More specifically, MPH did not show an effect on stimulus-related processes but modulated the onset latency of processes between stimulus evaluation and responding. These modulations were further shown to be associated with activation differences in the temporoparietal junction (BA40) and the superior parietal cortex (BA7) and may reflect neuronal gain modulation principles. The findings provide mechanistic insights into the role of modulated dopamine/norepinephrine transmitter systems for the interactions between perception and attention.

Influence of DARPP-32 genetic variation on BOLD activation to happy faces

Dopaminergic pathways play a crucial role in reward processing, and advanced age can modulate its efficiency. DARPP-32 controls dopaminergic function and is a chemical nexus of reward processing. In 61 younger (20–30 years) and older adults (54% ♀) (65–74 years), we examined how blood–oxygen-level dependent (BOLD) activation to emotional faces, vary over genotypes at three single nucleotide polymorphism (SNPs), coding for DARPP-32 (rs879606; rs907094; 3764352). We also assessed age-magnification of DARPP-32 effects on BOLD activation. We found that major homozygote G, T or A genotypes, with higher cortical expression of DARPP-32, higher dopamine receptor efficacy, and greater bias toward positive cues, had increased functional connectivity in cortical–subcortical circuits in response to happy faces, engaging the dorsal prefrontal cortex (DLPFC), fusiform gyrus (FG) and the midbrain (MB). Local BOLD response to happy faces in FG, and MB was age-dependent, so that older carriers of the major G, T or A alleles showed lesser activation than minor genotypes. These genetic variants of DARPP-32 did not modulate BOLD response to angry faces, or engagement of the inferior occipital gyrus, to happy or angry faces. Taken together our results lend support for a potential role of DARPP-32 genetic variants in neural response to potential reward triggering cues.

Perception in attention deficit hyperactivity disorder

A large body of research demonstrated that individuals with attention deficit hyperactivity disorder (ADHD) suffer from various neuropsychological deficits. In contrast, less is known and only divergent evidence exists on perceptual functions of individuals with ADHD. This is problematic as neuropsychological and perceptual functions are closely interrelated and are often difficult to disentangle in behavioral assessments. This study presents the conduct and results of a systematic literature review on perceptual functions in children and adults with ADHD. This review considers studies using psychophysical methods (objective measurements) and self- and informant reports (subjective measurements). Results indicate that individuals with ADHD have altered perceptual functions in various domains as compared to typically developing individuals. Increased perceptual functions in individuals with ADHD were found with regard to olfactory detection thresholds, whereas reduced perceptual functions were evident for aspects of visual and speech perception. Moreover, individuals with ADHD were found to experience discomfort to sensory stimuli at a lower level than typically developing individuals. Alterations of perceptual functions in individuals with ADHD were shown to be moderated by various factors, such as pharmacological treatment, cognitive functions, and symptom severity. We conclude by giving implications for daily life functioning and clinical practice.

Conflict processing in juvenile patients with neurofibromatosis type 1 (NF1) and healthy controls - Two pathways to success

Neurofibromatosis Type 1 (NF1) is a monogenetic autosomal-dominant disorder with a broad spectrum of clinical symptoms and is commonly associated with cognitive deficits. Patients with NF1 frequently exhibit cognitive impairments like attention problems, working memory deficits and dysfunctional inhibitory control. The latter is also relevant for the resolution of cognitive conflicts. However, it is unclear how conflict monitoring processes are modulated in NF1. To examine this question in more detail, we used a system neurophysiological approach combining high-density ERP recordings with source localisation analyses in juvenile patients with NF1 and controls during a flanker task. Behaviourally, patients with NF1 perform significantly slower than controls. Specifically on trials with incompatible flanker-target pairings, however, the patients with NF1 made significantly fewer errors than healthy controls. Yet, importantly, this overall successful conflict resolution was reached via two different routes in the two groups. The healthy controls seem to arrive at a successful conflict monitoring performance through a developing conflict recognition via the N2 accompanied by a selectively enhanced N450 activation in the case of perceived flanker-target conflicts. The presumed dopamine deficiency in the patients with NF1 seems to result in a reduced ability to process conflicts via the N2. However, NF1 patients show an increased N450 irrespective of cognitive conflict. Activation differences in the orbitofrontal cortex (BA11) and anterior cingulate cortex (BA24) underlie these modulations. Taken together, juvenile patients with NF1 and juvenile healthy controls seem to accomplish conflict monitoring via two different cognitive neurophysiological pathways.

Dopaminergic Input to the Inferior Colliculus in Mice

The response of sensory neurons to stimuli can be modulated by a variety of factors including attention, emotion, behavioral context, and disorders involving neuromodulatory systems. For example, patients with Parkinson’s disease (PD) have disordered speech processing, suggesting that dopamine alters normal representation of these salient sounds. Understanding the mechanisms by which dopamine modulates auditory processing is thus an important goal. The principal auditory midbrain nucleus, the inferior colliculus (IC), is a likely location for dopaminergic modulation of auditory processing because it contains dopamine receptors and nerve terminals immunoreactive for tyrosine hydroxylase (TH), the rate-limiting enzyme in dopamine synthesis. However, the sources of dopaminergic input to the IC are unknown. In this study, we iontophoretically injected a retrograde tracer into the IC of mice and then stained the tissue for TH. We also immunostained for dopamine beta-hydroxylase (DBH), an enzyme critical for the conversion of dopamine to norepinephrine, to differentiate between dopaminergic and noradrenergic inputs. Retrogradely labeled neurons that were positive for TH were seen bilaterally, with strong ipsilateral dominance, in the subparafascicular thalamic nucleus (SPF). All retrogradely labeled neurons that we observed in other brain regions were TH-negative. Projections from the SPF were confirmed using an anterograde tracer, revealing TH-positive and DBH-negative anterogradely labeled fibers and terminals in the IC. While the functional role of this dopaminergic input to the IC is not yet known, it provides a potential mechanism for context dependent modulation of auditory processing.

The Effects of Acute Dopamine Precursor Depletion on the Cognitive Control Functions of Performance Monitoring and Conflict Processing: An Event-Related Potential (ERP) Study

Studies using medications and psychiatric populations implicate dopamine in cognitive control and performance monitoring processes. However, side effects associated with medication or studying psychiatric groups may confound the relationship between dopamine and cognitive control. To circumvent such possibilities, we utilized a randomized, double-blind, placebo-controlled, within-subjects design wherein participants were administered a nutritionally-balanced amino acid mixture (BAL) and an amino acid mixture deficient in the dopamine precursors tyrosine (TYR) and phenylalanine (PHE) on two separate occasions. Order of sessions was randomly assigned. Cognitive control and performance monitoring were assessed using response times (RT), error rates, the N450, an event-related potential (ERP) index of conflict monitoring, the conflict slow potential (conflict SP), an ERP index of conflict resolution, and the error-related negativity (ERN) and error positivity (Pe), ERPs associated with performance monitoring. Participants were twelve males who completed a Stroop color-word task while ERPs were collected four hours following acute PHE and TYR depletion (APTD) or balanced (BAL) mixture ingestion in two separate sessions. N450 and conflict SP ERP amplitudes significantly differentiated congruent from incongruent trials, but did not differ as a function of APTD or BAL mixture ingestion. Similarly, ERN and Pe amplitudes showed significant differences between error and correct trials that were not different between APTD and BAL conditions. Findings indicate that acute dopamine precursor depletion does not significantly alter cognitive control and performance monitoring ERPs. Current results do not preclude the role of dopamine in these processes, but suggest that multiple methods for dopamine-related hypothesis testing are needed.

Two dopamine receptors play different roles in phase change of the migratory locust

The migratory locust, Locusta migratoria, shows remarkable phenotypic plasticity at behavioral, physiological, and morphological levels in response to fluctuation in population density. Our previous studies demonstrated that dopamine (DA) and the genes in the dopamine metabolic pathway mediate phase change in Locusta. However, the functions of different dopamine receptors in modulating locust phase change have not been fully explored. In the present study, DA concentration in the brain increased during crowding and decreased during isolation. The expression level of dopamine receptor 1 (Dop1) increased from 1 to 4 h of crowding, but remained unchanged during isolation. Injection of Dop1 agonist SKF38393 into the brains of solitary locusts promoted gregarization, induced conspecific attraction-response and increased locomotion. RNAi knockdown of Dop1 and injection of antagonist SCH23390 in gregarious locusts induced solitary behavior, promoted the shift to repulsion-response and reduced locomotion. By contrast, the expression level of dopamine receptor 2 (Dop2) gradually increased during isolation, but remained stable during crowding. During the isolation of gregarious locusts, injection of Dop2 antagonist S(–)-sulpiride or RNAi knockdown of Dop2 inhibited solitarization, maintained conspecific attraction-response and increased locomotion; by comparison, the isolated controls displayed conspecific repulsion-response and weaker motility. Activation of Dop2 in solitary locusts through injection of agonist, R(-)-TNPA, did not affect their behavioral state. Thus, DA-Dop1 signaling in the brain of Locusta induced the gregariousness, whereas DA-Dop2 signaling mediated the solitariness. Our study demonstrated that Dop1 and Dop2 modulated locust phase change in two different directions. Further investigation of Locusta Dop1 and Dop2 functions in modulating phase change will improve our understanding of the molecular mechanism underlying phenotypic plasticity in locusts.

Dopamine receptor D4 (DRD4) gene modulates the influence of informational masking on speech recognition

Listeners vary substantially in their ability to recognize speech in noisy environments. Here we examined the role of genetic variation on individual differences in speech recognition in various noise backgrounds. Background noise typically varies in the levels of energetic masking (EM) and informational masking (IM) imposed on target speech. Relative to EM, release from IM is hypothesized to place greater demand on executive function to selectively attend to target speech while ignoring competing noises. Recent evidence suggests that the long allele variant in exon III of the DRD4 gene, primarily expressed in the prefrontal cortex, may be associated with enhanced selective attention to goal-relevant high-priority information even in the face of interference. We investigated the extent to which this polymorphism is associated with speech recognition in IM and EM conditions. In an unscreened adult sample (Experiment 1) and a larger screened replication sample (Experiment 2), we demonstrate that individuals with the DRD4 long variant show better recognition performance in noise conditions involving significant IM, but not in EM conditions. In Experiment 2, we also obtained neuropsychological measures to assess the underlying mechanisms. Mediation analysis revealed that this listening condition-specific advantage was mediated by enhanced executive attention/working memory capacity in individuals with the long allele variant. These findings suggest that DRD4 may contribute specifically to individual differences in speech recognition ability in noise conditions that place demands on executive function.

Sources of pathology underlying listening disorders in children

Some children referred to audiology and developmental disability services have listening difficulties, despite normal audiograms. These children may be tested for 'auditory processing disorder' (APD), a controversial construct suggesting that neural dysfunction in the central auditory system leads to impaired auditory perception. An important question, not currently tested in clinical evaluation, is whether listening difficulties result from problems with bottom-up auditory sensory processing or top-down modulating cognition. Perceptual variability and poor performance on standardized tests suggest that listening difficulties are primarily cognitive in origin. However, evidence for impaired olivocochlear function and temporal processing deficits may implicate peripheral or central auditory dysfunction in some cases. Wide-spread, top-down modulation of auditory cortical, brainstem and ear function suggests that afferent and efferent control systems may not be simple to segregate. During normal maturation, hearing appears to develop in proportion to the complexity of both stimuli and tasks. But some younger individuals have mature hearing, highlighting individual differences that suggest APD may be due to a generalized developmental delay. Recent studies have investigated specific hypotheses showing, for example, that spatial hearing and executive function are compromised in some children with listening difficulties. Using speech stimuli (e.g. consonant-vowel syllables) to examine auditory brainstem responses, and psychophysiological relations between dichotic hearing and cortical physiology, various effects of auditory experience and development point the way to promising approaches for further studies of APD. Newer technology, from genetic sequencing to MRI, may have the sensitivity to test whether and how frequently APD is associated with impaired processing in the auditory system.

Interactive effects of KIBRA and CLSTN2 polymorphisms on episodic memory in old-age unipolar depression

The KIBRA (rs17070145) C-allele and the CLSTN2 (rs6439886) T-allele have both been associated with poorer episodic memory performance. Given that episodic memory is affected in depression, we hypothesized that the combination of these risk alleles would be particularly detrimental to episodic memory performance in depressed persons. In the population-based SNAC-K study, 2170 participants (≥ 60 years) without dementia (DSM-IV criteria) and antidepressant pharmacotherapy were clinically examined and diagnosed following ICD-10 criteria for unipolar depression, and genotyped for KIBRA and CLSTN2. Participants were categorized according to unipolar depression status (yes, no) and genotype combinations (KIBRA: CC, any T; CLSTN2: TT, any C). Critically, a three-way interaction effect showed that the CC/TT genotype combination was associated with poorer episodic recall and recognition performance only in depressed elderly persons, with depressed CC/TT carriers consistently performing at the lowest level. This finding supports the view that effects of genetic polymorphisms on cognitive functioning may be most easily disclosed at suboptimal levels of cognitive ability, such as in old-age depression.

Mouse social stress induces increased fear conditioning, helplessness and fatigue to physical challenge together with markers of altered immune and dopamine function

In neuropsychiatry, animal studies demonstrating causal effects of environmental manipulations relevant to human aetiology on behaviours relevant to human psychopathologies are valuable. Such valid models can improve understanding of aetio-pathophysiology and preclinical discovery and development of new treatments. In depression, specific uncontrollable stressful life events are major aetiological factors, and subsequent generalized increases in fearfulness, helplessness and fatigue are core symptoms or features. Here we exposed adult male C57BL/6 mice to 15-day psychosocial stress with loss of social control but minimal physical wounding. One cohort was assessed in a 3-day test paradigm of motor activity, fear conditioning and 2-way avoid-escape behaviour on days 16-18, and a second cohort was assessed in a treadmill fatigue paradigm on days 19 and 29, followed by the 3-day paradigm on days 30-32. All tests used a physical aversive stimulus, namely mild, brief electroshocks. Socially stressed mice displayed decreased motor activity, increased fear acquisition, decreased 2-way avoid-escape responding (increased helplessness) and increased fatigue. They also displayed increased plasma TNF and spleen hypertrophy, and adrenal hypertrophy without hyper-corticoidism. In a third cohort, psychosocial stress effects on brain gene expression were assessed using next generation sequencing. Gene expression was altered in pathways of inflammation and G-protein coupled receptors in prefrontal cortex and amygdala; in the latter, expression of genes important in dopamine function were de-regulated including down-regulated Drd2, Adora2a and Darpp-32. This model can be applied to identify targets for treating psychopathologies such as helplessness or fatigue, and to screen compounds/biologics developed to act at these targets.