Structural Directional Brain Behavior Asymmetry Across Cortical and Non-Cortical Regions

A substantial body of research suggests that the left and right cerebral hemispheres play differential roles in shaping human behavior. However, due to methodological considerations, most studies in this field have relied primarily on psychological methods. Here, we present exploratory neurobiological evidence suggesting that brain volume across numerous cortical and non-cortical homotopic regions may display consistent directional asymmetry in relation to a wide range of behavioral measures. Of particular note, such asymmetry recurred between contralateral homotopic areas across many behavioral parameters. The asymmetric behavioral directionality is distributed across most regions of the human brain, especially in the frontal and temporal cortices, which are particularly developed in humans. This may add a new dimension to previously described aspects of hemispheric asymmetry. In addition, it may help to understand why a marked functional asymmetry can be observed even when structural asymmetry is subtle. Moreover, these findings may shed light on how the brain modulates behavior in health and disease and may contribute to understanding processes involved in neurological and psychiatric disorders.