reorganized, while NMDA receptors in the CA1 are required in the acquisition and retrieval of memory after a delay, as well as in the formation of CA1 place fields. Blockade of the NMDA receptors prevents induction of long-term potentiation and impairs spatial learning. The CA3 of the hippocampus plays an especially important role in the encoding and retrieval of spatial memories. The CA3 is innervated by two afferent paths known as the perforant path (PPCA3) and the dentate gyrus (DG)-mediated mossy fibers (MFs). The first path is regarded as the retrieval index path while the second is concerned with encoding. Disorders/deficits Topographical disorientation Topographical disorientation (TD) is a cognitive disorder that results in the individual being unable to orient his or herself in the real or virtual environment. Patients also struggle with spatial-information dependent tasks. These problems could possibly be the result of a disruption in the ability to access one's cognitive map, a mental representation of the surrounding environment or the inability to judge objects' location in relation to one's self. Developmental topographical disorientation (DTD) is diagnosed when patients have shown an inability to navigate even familiar surroundings since birth and show no apparent neurological causes for this deficiency such as lesioning or brain damage. DTD is a relatively new disorder and can occur in varying degrees of severity. A study was done to see if topographical disorientation had an effect on individuals who had mild cognitive impairment (MCI). The study was done by recruiting forty-one patients diagnosed with MCI and 24 healthy control individuals. The standards that were set for this experiment were: Subjective cognitive complaint by the patient or his/her caregiver. Normal general cognitive function above the 16th percentile on the Korean version of the Mini-Mental State Examination (K-MMSE). Normal activities of daily living (ADL) assessed both clinically and on a standardized scale (as described below). Objective cognitive decline below the 16th percentile on neuropsychological tests. Exclusion of dementia. TD was assessed clinically in all participants. Neurological and neuropsychological evaluations were determined by a magnetic imaging scan which was performed on each participant. Voxel-based morphometry was used to compare patterns of gray-matter atrophy between patients with and without TD, and a group of normal controls. The outcome of the experiment was that they found TD in 17 out of the 41 MCI patients (41.4%). The functional abilities were significantly impaired in MCI patients with TD compared to