Neural stimulation Penfield was a groundbreaking researcher and original surgeon. His development of a neurosurgical technique using an instrument known as the Penfield dissector, which produced the least injurious
meningo-cerebral scar, became widely accepted in the field of neurosurgery and remains in regular use. With his colleague
Herbert Jasper, he invented the "Montréal Procedure" in which he treated patients with severe
epilepsy by destroying nerve cells in the
brain where the seizures originated. Before operating, he stimulated the brain with electrical probes while the patients were conscious on the operating table (under only
local anesthesia), and observed their responses. In this way he could more accurately target the areas of the brain responsible, reducing the
side-effects of the surgery. This technique also allowed him to create maps of the
sensory and
motor cortices of the brain (see
cortical homunculus) showing their connections to the various limbs and organs of the body. These maps are still used today, practically unaltered. Along with
Herbert Jasper, he published this work in 1951 (2nd ed., 1954) as the landmark
Epilepsy and the Functional Anatomy of the Human Brain. This work contributed a great deal to understanding the
localization of brain function. Penfield's maps showed considerable overlap between regions (e.g. the motor region controlling muscles in the hand sometimes also controlled muscles in the upper arm and shoulder) a feature which he put down to individual variation in brain size and localisation: it has since been established that this is due to the fractured
somatotopy of the motor cortex. From these results he developed his cortical homunculus map, which is how the brain sees the body from an inside perspective. Penfield reported that stimulation of the
temporal lobes could lead to vivid recall of memories. Oversimplified in popular psychology publications, including the best-selling ''
I'm OK – You're OK'', this seeded the common misconception that the brain continuously "records" experiences in perfect detail, although these memories are not available to conscious recall. Reported episodes of recall occurred in less than five percent of his patients, though these results have been replicated by modern surgeons. Penfield's hypothesis on this subject was revised in 1970.
Hallucinations Penfield's scientific contributions go past the
somatosensory and the
motor cortices; his extensive work of the functions of the brain also included charting the functions of the
parietal and
temporal cortices. Of his 520 patients, 40 reported that while their temporal lobe was stimulated with an electrode they would recall dreams, smells,
visual and
auditory hallucinations, as well as
out-of-body experiences. In his studies, Penfield found that when the
temporal lobe was stimulated it produced a combination of hallucinations, dream, and memory recollection. These experiences would only last as long as the electrode stimulations were present on the cortex, and in some cases when patient experienced hallucinatory experiences that evoked certain smells, sensations of flashing light, stroking the back of their hand, and many others. Other stimulations had patients experiencing
déjà vu, fear, loneliness, and strangeness. Certain areas of patients' temporal lobes were stimulated with an electrode in order to experience memories. Penfield called these perceptual illusions (physical hallucinations) interpretive responses. According to Penfield, when the temporal lobe was stimulated there were two types of perceptions experienced by patients: • Experential experience – where the patient recorded hearing a song, or seeing a flash of light. • Strip experience – The recall seems familiar to the patient and comes from the patient's past even though the patient may not be able to pinpoint the exact occasion. The recall of a memory or memories could reinforce the emotion tied to the experience. Penfield stressed that the "things that have been recorded are the things which once came within the spot-light of attention".
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 and 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 have 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 have
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. == Global policy ==