Neurobiological Convergence in SPDs and ADHD: Insights from a Narrative Review

The sensory system plays a critical role in the development since it allows us to correct and process the internal-external interaction, through the detection and encoding of the external stimuli. Dysfunctions of this system lead to the sensory integration, thus to the sensory processing disorders (SPDs). PSD affects about 5%–13% of 4-6-year-old children affecting not just their ability to respond to sensory information from the en-vironment, but also their social interaction and regulation of emotions, as well as the motor actions, learning, attention, communication, and sleep. SPDs have been extensively studied under different aspects, from molecular to behavioural ones, but the pathological mechanisms still remain under debate. Moreover, while there are many studies investigating the behavioural consequences of SPDs, which are used for diagnostic purposes, more are needed to find biomarkers. Indeed, since SPDs are often misdiagnosed with behaviour-related dysfunction, e.g., autism spectrum disorder, it is urgent to develop a new diagnostic tool, therefore targeting therapies. SPDs are misdiagnosed with attention deficit hyperactivity disorder (ADHD). Nevertheless, despite their similarity in behavioural symptoms and consequences, they have different causes, involve different neuronal circuits, and therefore have different treatments. In this narrative review, we aim to provide an overview of the literature on molecular and neuroimaging findings about SPDs. We will concentrate on the interaction between SPDs and ADHD, highlight the similarities and the differences, to more deeply understand the differences in pathological mechanisms and, in turn to highlight unique possible biomarkers, diagnostic and therapeutic tools.