Neural correlates of recovery from aphasia after damage to left inferior frontal cortex

Objective: To determine neural correlates of recovery from aphasia after le ft frontal injury. Methods: The authors studied the verbal performance of p atients with infarcts centered in the left inferior frontal gyrus (IFG), us ing a battery of attention-demanding lexical tasks that normally activate t he left IFG and a simpler reading task that does not normally recruit the l eft IFG. The authors used positron emission tomography (PET) and functional MRI (fMRI) to record neural activity in the same group of patients during word-stem completion, one of the attention-demanding lexical tasks. To iden tify potential neural correlates of compensation/recovery, they analyzed th e resulting data for the group as a whole (PET, fMRI) and also for each par ticipant (fMRI). Results: Patients with damage to the left IFG were impaire d on all attention-demanding lexical tasks, but they completed the word-rea ding tasks normally. The imaging studies demonstrated a stronger-than-norma l response in the right IFG, a region homologous to the damaged left IFG. T he level of activation in the right IFG did not correlate with verbal perfo rmance, however. In addition, a perilesional response within the damaged le ft IFG was localized in the two patients who gave the best performance in t he word-stem completion task and showed the most complete recovery from aph asia. Conclusions: Right-IFG activity may represent either the recruitment of a preexisting neural pathway through alternative behavioral strategies o r an anomalous response caused by removal of the left IFG. Perilesional act ivity in the left IFG may represent sparing or restoration of normal functi on in peri-infarctual tissue that was inactive early on after injury. This activity may be of greater functional significance than right IFG activity because it was associated with more normal verbal performance.