Inclusion Criteria:

1. Age: Individuals aged 18-60 who sustained a mild to moderate TBI 6-12 months prior to study entry.
2. TBI: The minimum level of injury severity included will be based on the criteria established by the American Congress of Rehabilitative Medicine for mild brain injury. Specifically, subjects must sustain a traumatic blow to the head, resulting in either alteration of level of consciousness (manifested by being dazed and confused and having amnesia for the event) or loss of consciousness (LOC). The upper limit of severity will be the commonly accepted criteria for moderate traumatic brain injuries; trauma resulting in LOC of up to 60 minutes, and ED Glasgow Coma Scale (GCS) scores of 9-12. Duration of LOC will be estimated by using all available information including patient and witness reports, emergency personnel records and DHMC medical records. PTA will be estimated by careful questioning of patients to determine the time of return of continuous memory. This will be informed by review of medical records. We plan to include individuals with intracranial or skull injuries stemming from the TBI, providing they meet the inclusion criteria. Such lesions will be catalogued, and included as a factor in the data analysis. Large structural pathology with lobar deformations or midline shift will be exclusions.
3. Cognitive Deficits: Subjects will have both subjective and objective evidence of persistent cognitive deficits. Subjects must report persistent memory or attention deficits as a result of their injury, which are of sufficient severity to interfere with social and/or occupational functioning. Subjects must either score more than 2 standard deviations below the age adjusted norm or estimates of baseline premorbid function (using the Barona Index) on one or more tests of attention and/or memory administered as part of the baseline screening cognitive battery (see below), or score greater than 1.0 standard deviations below either age adjusted norms or estimates of premorbid function on 2 or more of the screening tests (see below).

Exclusion Criteria:

The following factors will exclude otherwise eligible subjects from participation:

1. a history of other neurologic disorders (such as epilepsy, cerebrovascular disease, mental retardation, neurodegenerative disorders)
2. significant systemic medical illness such as clinically significant liver disease, renal disease, atherosclerotic coronary vascular disease, or hypertension requiring medication management
3. current DSM-IV Axis I diagnosis of psychiatric illness other than substance abuse. We have given careful consideration to the inclusion of the latter group given our use of a stimulant with potential abuse properties. Because of the potential for cross-over abuse with cocaine, amphetamines, and other stimulants, individuals with such histories will be excluded from this study. Individuals with history of otherwise uncomplicated ethanol or other non-stimulant drug abuse currently in stable remission will be eligible. The Structured Clinical Interview for DSM-IV (SCID) will be used to screen for psychiatric illness
4. women currently pregnant or lactating. Female participants will be asked to take a pregnancy test to confirm they are not currently pregnant.