Differential SPECT Activation Patterns Associated with PASAT Performance May Indicate Frontocerebellar Functional Dissociation in Chronic Mild Traumatic Brain Injury

Patients with mild traumatic brain injury (TBI) often complain of cognitive fatigue during the chronic recovery phase. The Paced Auditory Serial Addition Test (PASAT) is a complex psychologic measure that may demonstrate subtle deficiencies in higher cognitive functions. The purpose of this study was to investigate the brain activation of regional cerebral blood flow (rCBF) with PASAT in patients with mild TBI to explore mechanisms for the cognitive fatigue. Methods: Two groups consisting of 15 patients with mild TBI and 15 healthy control subjects underwent Tc-99m-ethylene cysteine dimer SPECT at rest and during PASAT on a separate day. Cortical rCBF was extracted using a 3-dimensional stereotactic surface projection and statistically analyzed to identify areas of activation, which were compared with PASAT performance scores. Results: Image analysis demonstrated a difference in the pattern of activation between patients with mild TBI and healthy control subjects. Healthy control subjects activated the superior temporal cortex (Brodmann area [BA] 22) bilaterally, the precentral gyrus (BA 9) on the left, and the precentral gyrus (BA 6) and cerebellum bilaterally. Patients with mild TBI demonstrated a larger area of supratentorial activation (BAs 9, 10, 13, and 46) but a smaller area of activation in the cerebellum, indicating frontocerebellar dissociation. Conclusion: Patients with mild TBI and cognitive fatigue demonstrated a different pattern of activation during PASAT. Frontocerebellar dissociation may explain cognitive impairment and cognitive fatigue in the chronic recovery phase of mild traumatic brain injury.