THE BEHAVIORAL HEALTH AND PERFORMANCE (BHP) ELEMENT OF THE NASA HUMAN RESEARCH PROGRAM (HRP) DEFINES THE PREVENTION OF ADVERSE HEALTH CONSEQUENCES INCLUDING NEUROCOGNITIVE IMPAIRMENT AS ONE OF THE KEY MILESTONES OF ARTIFICIAL GRAVITY (AG) COUNTERMEASURE DEVELOPMENTS. REMARKABLY THE NEUROPHYSIOLOGICAL CORRELATE OF COGNITIVE PERFORMANCE CHANGES (ESPECIALLY SPATIAL COGNITION) ASSOCIATED WITH AG HAS RECEIVED LITTLE ATTENTION. IN FACT RESEARCH ON THE EFFECTS OF INTERMITTENT AG ON STRUCTURAL AND FUNCTIONAL CHANGES OF THE BRAIN IS PRESENTLY LACKING COMPLETELY. WHILE THE ENTIRE BRAIN MAY BE PRONE TO STRUCTURAL AND FUNCTIONAL CHANGES AS A RESULT OF BODY UNLOADING AND AG THE HIPPOCAMPAL FORMATION - A KEY AREA FOR THE BRAIN FOR MEMORY FORMATION AND SPATIAL NAVIGATION AND ONE OF THE ONLY TWO HUMAN BRAIN AREAS EXHIBITING NEUROGENESIS - IS EXPECTED TO BE HIGHLY VULNERABLE TO STRESS AND A KEY TARGET FOR MITIGATING NEUROCOGNITIVE IMPAIRMENTS. THE OVERARCHING GOAL OF THE PRESENT PROPOSAL IS THEREFORE TO QUANTIFY THE EFFECTS OF DIFFERENT PROTOCOLS OF INTERMITTENT AG DURING 60 DAYS OF HDBR ON CORTICAL NEUROPLASTICITY RELATED TO BEHAVIORAL OUTCOMES ASSOCIATED WITH NEURAL CONTROL OF THE CARDIOVASCULAR SYSTEM AND SPATIAL COGNITION AND BIOCHEMICAL CORRELATES. USING STATEOF- THE ART NEUROIMAGING ULTRASOUND IMAGING AND COGNITIVE TOOLS MEASURES MADE IN HDBR PARTICIPANTS WILL BE CONTRASTED WITH A CONTROL GROUP MATCHED FOR GENDER AGE AND EDUCATIONAL BACKGROUND. THE DATA WILL ALSO BE COMPARED TO DATA FROM TWO ADDITIONAL ESA HDBR STUDIES OF THE SAME LENGTH AS WELL AS DATA OBTAINED FROM LONG-DURATION ISS MISSIONS ANTARCTIC EXPEDITIONS AND HERA ISOLATION STUDIES. THESE STUDIES EMPLOY VERY SIMILAR PROCEDURES THAT ALLOW COMPARING THE EFFECTIVENESS OF AG TO EXERCISE AS WELL AS TO NUTRITIONAL COUNTERMEASURES. AT THE END OF THE PROJECT WE WILL HAVE A CLEAR UNDERSTANDING WHETHER AND TO WHAT EXTENT ANY EFFECTS ON NEUROPLASTICITY AND BEHAVIORAL HEALTH ASSOCIATED WITH HDBR CAN BE AUGMENTED BY A CENTRIFUGATION COUNTERMEASURE.