| Functional reorganization in poststroke aphasia is not well understood. For nearly a century and a half, studies have explored correlations between sites of lesion and language loss and recovery, making significant contributions to our understanding of hemispheric lateralization and localization of function. Still, our knowledge of the dynamic complexity of reorganization of function has remained elusive.; Recent investigations utilizing functional neuroimaging to examine cortical plasticity have shed light on compensatory mechanisms for coping with brain damage. Only a small percentage of these studies have investigated the neural mechanisms underlying language recovery in severe aphasia patients, who are typically viewed as having a poor prognosis for language recovery, with severely limited, and at times unreliable, expressive output.; The purpose of this study was to investigate functional reorganization in severe nonfluent aphasia. Functional MRI was utilized to image four chronic, moderate-to-severe patients and four healthy age- and gender-matched controls during nonverbal, two-choice button-box decisions regarding semantic relatedness of objects and of actions and objects. Tasks were designed using images of common, familiar, concrete objects and picturable actions. Contrasts examined differences in activation between Animals/Tools, Objects/Actions, Easy/Difficult conditions, and Correct/Incorrect trials.; As predicted, there was considerable individual variability in patterns of activation and behavioral responses. Both were modulated by task difficulty. Normal controls (NCs) activated broad semantic networks, including left perisylvian and bilateral visual association regions previously associated with semantic decision-making. Patients demonstrated variability in the degree to which activations resembled subsets of NC activations and in the amount and location of right hemisphere and perilesional recruitment. Some patterns appeared to be indicative of brain reorganization for language recovery, while others may reflect persistence of, rather than recovery from, aphasia.; This study provides fMRI evidence of the necessary and sufficient neural substrates underlying nonverbal semantic processing, including the effects that category, task difficulty, and making of errors have on patterns of activation. Often attempts are made to train patients with severe nonfluent aphasia to use icon-based communication systems which place high demands on nonverbal semantic processing. A better understanding of healthy and recovering distributed semantic networks could have clinical implications for these patients. |
