Déjà vu
Penfield's expansion of the interpretive cortex includes the phenomenon of "déjà vu". "Déjà vu" is the sensation that an experience a person is having has previously been experienced. "Déjà vu" is typically experienced by people between the ages of 15 to 25, and affects approximately 60-70% of the population. It is thought to be a mismatch of the sensory input people receive and the system in which the brain recalls memory. Another thought on the cause of "déjà vu" is that there is a malfunction in the brain's short- and long-term memory systems where memories become stored in incorrect systems. There are several ways one can recognize familiar experiences – by mentally retrieving memories of a previous experience, or by having a feeling that an experience has occurred when it actually has not. "Déjà vu" is having that feeling of familiarity in a situation that is completely new. Memory is good at being familiar with objects, however it does not do well with the configuration or organization of objects. "Déjà vu" is an extreme reaction to the mind telling an individual that they are having a familiar experience. "Déjà vu" is thought to be a consistent phenomenon. However, it has been associated with epilepsy, and with multiple psychiatric disorders such as schizophrenia and anxiety, but there has not been a clear, frequent diagnostic correlation between "déjà vu" and neurological or psychiatric disorders, except with patients that have a possibility of being epileptic. Temporal lobe epilepsy affects the hippocampus. Patients that suffer from this medical diagnosis are said to have a misfiring of the brain's neurons. The neurons transmit at random which results in the false sense of experiencing a familiar situation that had previously been experienced. Different types of "déjà vu" are difficult to pinpoint because researchers who have studied "déjà vu" have developed their own categories and differentiations. On a broad perspective of research that is available, "déjà vu" can be divided into two categories: associative "déjà vu" and biological déjà vu. Associative "déjà vu" is typically experienced by normal, healthy individuals who experience things with the senses that can be associated to other experiences or past events. Biological "déjà vu" occurs in individuals who suffer from temporal lobe epilepsy. Their experience of "déjà vu" occurs usually just before they experience a seizure. Recent research is looking at the new occurrence of chronic "déjà vu". Chronic "déjà vu" is when an individual is experiencing a constant state of "déjà vu". Failure of the temporal lobe is thought to be the cause of this phenomenon because the circuits that connect to memories get stuck in an active state, and create memories that never happened.