A computer-implemented system for providing a virtual reality environment for treatment or prevention of a neurological or psychiatric disorder, in particular Alzheimer, or cognitive deficits in normal aging by stimulating a targeted area of the brain, the system adapted to: - access at least one VR memory training module targeting at least one of the hippocampus and neighboring entorhinal cortex region of a participant's brain including one or more memory training tasks comprising interactive user controlled navigation tasks to be performed within a three- dimensional VR environment; - execute the at least one VR memory training module including one or more memory training tasks comprising interactive user controlled navigation tasks configured to train the participant's understanding of relationships between at least one of spatial and temporal details in the 3D VR environment in order to target the at least one of the hippocampus and neighboring entorhinal cortex region of the participant's brain and to display a 3D VR environment including one or more memory training tasks comprising interactive user controlled navigation tasks in order to stimulate and/or promote growth of grey matter in the hippocampus and neighboring entorhinal cortex region of the participant's brain; - receive an input from the participant via an interactive controller to assess the participant's understanding of relationships between the at least one of spatial and temporal details in the 3D VR environment in an alternate view; and - analyze the results of one or measurements of the participant's brain structure or brain activity before and after, or during the execution of the at least one VR memory training modules for evidence of the stimulation and/or promote growth of grey matter in the hippocampus and neighboring entorhinal cortex region of the participant's brain resulting from the execution of the one or more training tasks, wherein the measurement comprises a structural or functional magnetic resonance imaging scan or feedback from sensors indicating the level of brain activity in particular regions of the brain, whereby, the effectiveness of the at least one VR memory training module in targeting the at least one of the hippocampus and neighboring entorhinal cortex region of the participant's brain can be determined; and - based on this effectiveness, determine and/or amend the duration and difficulty of the subsequent VR memory training module. - access at least one VR memory training module targeting at least one of the hippocampus and neighboring entorhinal cortex region of a participant's brain including one or more memory training tasks comprising interactive user controlled navigation tasks to be performed within a three- dimensional VR environment; - execute the at least one VR memory training module including one or more memory training tasks comprising interactive user controlled navigation tasks configured to train the participant's understanding of relationships between at least one of spatial and temporal details in the 3D VR environment in order to target the at least one of the hippocampus and neighboring entorhinal cortex region of the participant's brain and to display a 3D VR environment including one or more memory training tasks comprising interactive user controlled navigation tasks in order to stimulate and/or promote growth of grey matter in the hippocampus and neighboring entorhinal cortex region of the participant's brain; - receive an input from the participant via an interactive controller to assess the participant's understanding of relationships between the at least one of spatial and temporal details in the 3D VR environment in an alternate view; and - analyze the results of one or measurements of the participant's brain structure or brain activity before and after, or during the execution of the at least one VR memory training modules for evidence of the stimulation and/or promote growth of grey matter in the hippocampus and neighboring entorhinal cortex region of the participant's brain resulting from the execution of the one or more training tasks, wherein the measurement comprises a structural or functional magnetic resonance imaging scan or feedback from sensors indicating the level of brain activity in particular regions of the brain, whereby, the effectiveness of the at least one VR memory training module in targeting the at least one of the hippocampus and neighboring entorhinal cortex region of the participant's brain can be determined; and - based on this effectiveness, determine and/or amend the duration and difficulty of the subsequent VR memory training module.