Although larger left amygdala volume is associated with ADHD, larger right amygdala volume is associated with impulsivity, a recent Spanish study reports.
This study aimed to investigate the hypothesis that smaller amygdala volume in patients with ADHD is related to impulsivity and emotional instability. Adults with ADHD (n=9; mean age 25.5 years) were enrolled from the ADHD unit of a general hospital and compared with adults without ADHD (n=9; mean age 25.17 years). Impulsivity was measured using the Barratt Impulsiveness Scale (BIS) prior to a magnetic resonance imaging (MRI) scan. Images of the brain were assessed using FIRST*, to obtain volume values for both hemispheres of the amygdala (left and right), measured in cubic millimetres. To account for variation in head size, SIENAX* software was used.
MRI results indicated that the average right amygdala volume was similar between adults with and without ADHD (1647mm3 vs 1543mm3, respectively; p=0.288), whilst left amygdala volume was significantly larger in adults with ADHD compared with adults without ADHD (1727mm3 vs 1515mm3, respectively; p=0.009). However, although a significant negative correlation between BIS score and right amygdala volume was noted (r=-0.756, p=0.018), there was no apparent correlation between BIS score and left amygdala volume.
Researchers concluded that left and right amygdala volumes have differential roles in the aetiology of ADHD, although future studies should use multimodal designs accounting for different ADHD symptoms and comorbidities to try and explain these contradictory findings.
Read more about the amygdala and its relationship with ADHD and impulsivity here
*FIRST and SIENAX are part of the FMRIB Software Library (FSL) of brain imaging analysis tools. FIRST is a model-based segmentation/registration tool used to determine the volume of several subcortical structures using brain imaging data, whilst SIENAX can normalise brain volumes according to head size.
Tajima-Pozo K, Ruiz-Manrique G, Yus M, et al. Correlation between amygdala volume and impulsivity in adults with attention-deficit hyperactivity disorder. Acta Neuropsychiatr 2015; 27: 362-367.