Disentangling early versus late audiovisual integration in adult ADHD: a combined behavioural and resting-state connectivity study

Abstract

Background: Studies investigating sensory processing in attention-deficit/hyperactivity disorder (ADHD) have shown altered visual and auditory processing. However, evidence is lacking for audiovisual interplay - namely, multisensory integration. As well, neuronal dysregulation at rest (e.g., aberrant within- or between-network functional connectivity) may account for difficulties with integration across the senses in ADHD. We investigated whether sensory processing was altered at the multimodal level in adult ADHD and included resting-state functional connectivity to illustrate a possible overlap between deficient network connectivity and the ability to integrate stimuli.

Methods: We tested 25 patients with ADHD and 24 healthy controls using 2 illusionary paradigms: the sound-induced flash illusion and the McGurk illusion. We applied the Mann-Whitney U test to assess statistical differences between groups. We acquired resting-state functional MRIs on a 3.0 T Siemens magnetic resonance scanner, using a highly accelerated 3-dimensional echo planar imaging sequence.

Results: For the sound-induced flash illusion, susceptibility and reaction time were not different between the 2 groups. For the McGurk illusion, susceptibility was significantly lower for patients with ADHD, and reaction times were significantly longer. At a neuronal level, resting-state functional connectivity in the ADHD group was more highly regulated in polymodal regions that play a role in binding unimodal sensory inputs from different modalities and enabling sensory-to-cognition integration.

Limitations: We did not explicitly screen for autism spectrum disorder, which has high rates of comorbidity with ADHD and also involves impairments in multisensory integration. Although the patients were carefully screened by our outpatient department, we could not rule out the possibility of autism spectrum disorder in some participants.

Conclusion: Unimodal hypersensitivity seems to have no influence on the integration of basal stimuli, but it might have negative consequences for the multisensory integration of complex stimuli. This finding was supported by observations of higher resting-state functional connectivity between unimodal sensory areas and polymodal multisensory integration convergence zones for complex stimuli.

Figure 1

(A) Sound-induced flash illusion. Upper left, fusion rates for the bimodal incongruent condition (1 flash/2 beeps); upper right, reaction times compared for the bimodal incongruent condition (1 flash/2 beeps) for integration and no integration; lower left, percentage of correct button presses for control conditions; lower right, reaction times for control conditions. (B) McGurk illusion. Left, comparison of responses to the bimodal incongruent condition: fused response (successful integration), auditory input (heard tone) or visual input (lip movements). Right, comparison of reaction times for successful integration (fused) or auditory or visual answers. *p = 0.05; **p = 0.01. B = beep; F = flash.

Figure 2

Correlation between CAARS inattention scores and fused (multisensory integration) responses to the McGurk illusion. ADHD = attention-deficit/hyperactivity disorder; CAARS = Conners’ Adult ADHD Rating Scale.

Figure 3

Linear regression with severity of childhood ADHD (WURS-k score) as a predictor of fused (multisensory integration) responses to the McGurk illusion. ADHD = attention-deficit/hyperactivity disorder; WURS-k = Wender Utah Rating Scale.

Figure 4

Resting-state functional connectivity. (A) Enhanced resting-state functional connectivity in patients with ADHD compared to healthy controls. (B) Correlation between McGurk scores and resting-state functional connectivity across the entire study sample. False discovery rate correction was applied at the cluster level (p < 0.05). ADHD = attention-deficit/hyperactivity disorder; IFG = inferior frontal gyrus; MTG = middle temporal gyrus; PaHC = parahippocampal gyrus.