Inclusion Criteria:

- Patients planned for radiosurgery for benign disorders (Groups 1&2).

- Patients planned for prophylactic cranial irradiation (Group 3)

Exclusion Criteria:

- Previous cranial radiation

- Severe psychiatric disorder

- Severe cognitive or memory impairment (MMSE < 21)

- Non-English speaking, which will potentially make memory testing difficult and
unreliable.

- Other medical conditions deemed by the PI or associates to make the patient
ineligible for protocol procedures

- Patients on steroid medications.

- Left hand dominant patients

- Dose exposure to left hippocampus >0.5Gy and <2Gy. We will attempt to estimate dose
to hippocampus prior to enrollment using pre-planning on diagnostic imaging to
minimize exclusion of patients due to dose exposure >0.5 Gy and < 2Gy following
baseline memory testing.

- Benzodiazepine or narcotics given on the day of radiotherapy/radiosurgery prior to
completion of the study procedures

- Previous brain surgery within one year prior to radiosurgery

- Pregnant women