Close your eyes and imagine home. Sharp details—such as the shape of the front doorknob, the height of the windows, or the paint color—assemble in your mind with a richness that seems touchable. A new study has found where this mental projection lives in the brain by inducing hallucinations in an epilepsy patient. A 22-year-old male was receiving deep brain stimulation to isolate where his daily seizures originated. His disorder appeared after he caught West Nile virus at the age of 10 and subsequently suffered from brain inflammation. His episodes were always preceded by intense déjà vu, suggesting a visual component of his disease, but he had no history of hallucinations. Brain scans revealed a shrunken spot near his hippocampus—the brain’s memory center. Studies had shown that this region—known as the parahippocampal place area (PPA)—was involved with recognizing of scenes and places. Doctors reconfirmed this by showing the patient pictures of a house and seeing the PPA light up on brain scans with functional magnetic resonance imaging (images above show brain activity; yellow indicates stronger activation than red). Thin wire electrodes—less than 2 mm thick—placed in the PPA (yellow dots in right panel) recorded similar brain activity after viewing these pictures. To assess if the PPA was ground zero for seizures, the doctors used a routine procedure that involves shooting soft jolts of electricity into the region and seeing if the patient senses an oncoming seizure. Rather than have déjà vu, the patient’s surroundings suddenly changed as he hallucinated places familiar to him. In one instance, the doctors morphed into the Italians from his local pizza place. Zapping a nearby cluster of neurons produced a vision of his subway station. The findings, published on 16 April in The Journal of Neuroscience, confirm that this small corner of the brain is not only responsible for recognizing places, but is also crucial to recalling a mental vision of that place.
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