Top-down information processing occurs when the brain forms perceptions based on already stored information, allowing for increased processing speeds when receiving information from a sensory stimulus. More specifically, this form of processing contextualizes information from generalizations based on expectations and prior experiences to generate more specific inferences. For example, if one is presented with an image displaying only half of a computer, they would use previous knowledge through top-down processing to fill in the rest of the image based on previous knowledge and expectations. Individuals with Attention-Deficit/Hyperactivity Disorder (ADHD), however, demonstrate deficiencies with top-down processing.
In the article, “Top-down attention modulates auditory-evoked neural responses in neurotypical, but not ADHD, young adults,” Kwasa et al. studied how individuals with ADHD demonstrate cognitive deficiencies with top-down processing when focusing attention on sensory stimuli. Specifically, the researchers investigated how these patients exhibit poorer performance compared to neurotypical individuals when completing tasks demanding of selectively attending to goal-relevant auditory stimulation - a challenging task requiring strong use of top-down attention. Participants listened to one of three concurrent, spatially separated streams of speech, and they were required to report the order of syllabi presented. As the participants were completing the task, the researchers were measuring electrophysiological correlates that are specific to top-down processing. Interestingly, they observed decreased N1 modulation (a negative-going ERP moment) in ADHD subjects compared to controls. Experimentation tested the ability to sustain attention on an individual speech stream as well as the ability to remain focused on the target while flexibly switching attention to a competing “interrupter” stimulus. According to the results of the study, attentional modulation indicative of top-down processing was weaker in participants with ADHD, demonstrating the differential abilities of listeners to modulate neural representations of sound with regard to the goals of the task.
This weaker modulation of individuals with ADHD may also be implicated in symptoms of other behavioral disorders. In a related research study, “Distinct brain structure and behavior related to ADHD and conduct disorder traits,” Bayard et al. studied the comorbidity and shared genetic features of top-down dysregulation found in individuals with ADHD and Conduct Disorder (CD). Elaborating on previous studies, the researchers examined both non-emotional and emotional dysregulation as related to the deficiencies found in top-down processing pathways. Using magnetic resonance imaging (MRI) techniques, results of the study demonstrated that both ADHD and CD symptoms were correlated with overlapping activity in specific brain structures, notably a small structure of the prefrontal and anterior cingulate cortex. The researchers found that the gray matter volume and surface area of the region of interest found in the dorsolateral/dorsomedial prefrontal cortex and caudal anterior cingulate cortex demonstrated a negative association with ADHD symptoms while CD symptoms were being controlled, and the gray matter volume of the rostral anterior cingulate cortex demonstrated a negative association to CD symptoms while ADHD symptoms were being controlled. Similar findings were found when the researchers administered tests that required activity of the prefrontal and anterior cingulate regions. These data elaborate on deficiencies in top-down processing; performance on a Stop Signal test was specifically correlated with ADHD, while working memory was implicated with both ADHD and CD. Thus, the top-down processing deficiencies observed in individuals with ADHD demonstrate partial domains and dimensional capacities in the associated processing regulatory system.
These two studies together provide greater insight into processing deficiencies associated with ADHD. Modulation of top-down processing involves varying domains and capacities that overlap with other neurological modalities, and the implications of the interactions of these pathways should be studied further.
References
Bayard F;Nymberg Thunell C;Abé C;Almeida R;Banaschewski T;Barker G;Bokde ALW;Bromberg U;Büchel C;Quinlan EB;Desrivières S;Flor H;Frouin V;Garavan H;Gowland P;Heinz A;Ittermann B;Martinot JL;Martinot MP;Nees F;Orfanos DP;Paus T;Poustka L;Conrod P;Stringari. (n.d.). Distinct brain structure and behavior related to ADHD and conduct disorder traits. Molecular psychiatry. Retrieved March 4, 2022, from https://pubmed.ncbi.nlm.nih.gov/30108313/
Kwasa, J. A., Noyce, A. L., Torres, L. M., & Shinn-Cunningham, B. G. (2021). Top-down attention modulates auditory-evoked neural responses in neurotypical, but not ADHD, young adults. https://doi.org/10.1101/2021.02.11.430824
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