Actual Experiments (And What They Have Found)
The amygdala and hippocampus. Image from http://www.humanillnesses.com/
Much of the research into artificially stimulating the temporal lobe has shown that this stimulation causes visual experiential responses and hallucinations in humans (Miyashita, 1993).Experimentally stimulating parts of the brain can be more localized than a seizure, which may be more widespread. Scientists have tried to determine which parts of the temporal lobe are responsible for different aspects of the behavioral responses during a seizure. Research has shown that both the medial and the lateral parts of the temporal lobe are involved in the experiential hallucinations associated with stimulation of the temporal lobe. The medial temporal lobe connects to the amygdala and the hippocampus, which are involved in emotions and memory. Stimulating these areas give the hallucination its realistic and emotional feeling. The lateral temporal lobe is also related to memory, and its stimulation can stimulate a hallucination of an actual memory (Fried, 1997).
In fact, in depth research has been done to try to localize which part of the phenomena are associated with temporal lobe seizures. A study done by Bancaud, Brunet-Bourgin, Chauvel, and Halgren (1994) studied patients who either had a spontaneous seizure, had electrical stimulation to imitate the effects of a seizure, or had chemical stimulation to imitate the effects of a seizure. Stimulating the neocortex (the main part of the brain), the amygdala or the hippocampus could produce hallucinations. When an illusion was stimulated in the medial temporal lobe (near the hippocampus and amygdala), the electrical effects in the brain spread outward to the outer part of the temporal lobe. When the illusion was caused by stimulation to the outer temporal lobe the electrical effects spread inward, but the event was smaller overall. This study concluded that these hallucinations and illusions are caused by electrical stimulation of a network of neurons that include much of the temporal lobe, the amygdala and the hippocampus (Bancaud, Brunet-Bourgin, Chauvel, & Halgren, 1994).
Electrodes in a human skull. Image courtesy of http://www.epilepsyfoundation.org
Mahl, Rothenberg, Delgado,
and Hamlin (1964) did a study that focused on the effects of stimulating
the temporal lobe of a twenty-seven year old woman with a history of
temporal lobe seizures. Her seizures had three components: she
would get a "funny feeling," her perception of the world changed
(it became dull and unfamiliar and she could not read print on a page),
and a blank period of time when she could not see or hear people.
She was admitted to the hospital because of her seizures, and for this
study electrodes were implanted in her brain. One researcher would
interview her while the electrodes were stimulating her brain to note
the behavioral changes that accompanied the stimulation. Interviews were also done when her brain was not being stimulated, so that the researchers could compare her behaviors in both situations.
What they found was that stimulation regularly produced sensations that
she was experiencing something. Visually she experienced hallucinations
and illusions, and she also experienced an increase in her use of words.
The researchers also noted that most of these experiences were a result
of artificial stimulation (as opposed to spontaneous seizure activity).
They also found that often the experiences were related to the content
of the interview. These researchers concluded that stimulation
of the left temporal lobe produces complex responses from hallucinations
to nonsensical speech (Mahl, Rothenberg, Delgado, & Hamlin, 1964).
Research has also been done
stimulating the temporal lobes of monkeys. A study done by DeAngelis,
Cumming, and Newsome (1998) focused on stimulating a very specific part
of the temporal lobe known to be related to perceiving motion.
These researchers found that this part of the temporal lobe is also
important in depth perception. Using small electrodes implanted
in the monkeys' brains they electrically stimulated this very specific
part of the temporal lobe, and they found that other parts of the temporal
lobe responded as well. They also studied monkeys' responses
to visual tasks that required depth perception. They found that
when this part of the brain was stimulated it affected how the monkeys
performed on the depth perception task. These findings indicate
that this part of the brain is not only involved in the perception of
movement, but also in depth judgments (DeAngelis, Cumming, &Newsome,
Case 1: One man, with a history of epilepsy underwent a number of surgeries one of which involved implanting electrodes in his brain. They were located in the temporal lobe. The man had a history of many seizures in the temporal lobe area. When the electrodes were implanted they were used to stimulate the temporal lobe. The patient noted that when the electrodes were stimulated he had two distinct hallucinations of events that had to do with things that occured earlier in the day. He saw red blocks that he associated with a psychological test he had recently undergone, and he saw a nurse standing at the end of the bed. Further surgery revealed that this patient had damage to his temporal lobe caused by the seizures.
Case 2: Another patient,
also with a history of epilepsy was brought to the hospital for surgery
for his seizures. He too had electrodes implanted. When
his electrodes were stimulated he hallucinated a scene with green water,
small people fishing off of a pier, and a Howard Johnson restaurant.
These hallucinations could be related to an earlier conversation that
he had had with an interviewer. It also related to a childhood
memory of fishing near a Howard Johnson restaurant (Ferguson, et al., 1969).
Case 3: A patient whose
temporal lobe was being stimulated so that his doctors could map his
temporal cortex and localize when and where his seizures started also
reported a number of hallucinationsHe heard the theme music
from Star Wars, and he reported seeing birds and experiencing
the sensation of going through a tunnel. As the stimulation continued
he also reported seeing an angel on a Christmas tree, hearing wedding
music and bells, and seeing a wedding scene. The patient was aware
that these scenes were not real and they were not directly memories
from a specific event (Fried, 1997).