Morphologic Studies

Anatomic Studies

Morphologic analyses have revealed symmetry of the frontal lobes in patients with AD/HD instead of the normal right greater than left pattern. The morphologic studies have also revealed a smaller left caudate and globus pallidus in patients with AD/HD (28, 29)

Positron Emission Scanning

Glucose metabolism in the adults with residual type AD/HD has been measured by PET scan and was found to be globally decreased. Four regions of the brain showed significantly lower metabolism in patients compared to controls. These areas were located primarily in the premotor and somatosensory cortex of the frontal lobe(26). However, subsequent studies in adolescents with AD/HD have not confirmed these findings(50).

Click HERE to view a PET scan of an adult with residual type AD/HD.

 

Blood Flow Analysis

Alterations in blood flow to the frontal and basal ganglia regions have been reported in patients with AD/HD. These abnormalities of flow are reversed by treatment with methylphenidate (27).


Clinical Correlation

The right hemisphere may be dominant for mediating attention. Left hemisphere lesions are associated with no effect on attention. However, lesions of the right hemisphere will induce severe inattention and an inability to sustain simple motor acts (30).

Lesions of the medial and dorsolateral frontal lobes are associated with inattention, impaired response inhibition and motor impersistence. The right frontal lobe and right striatum appear to be particularly important for inhibiting unwanted action in response to stimuli (31, 32).

Prefrontal damage is known to cause disturbance in drive and executive control. This lack of executive control results in impulsive actions do to an inability to think ahead to the consequences of an action(33).