TLE
Artificial Stimulation of the Temporal Lobe
Mechanisms of Artificial Stimulation
This page intends to look into the research that has been done with stimulating the temporal lobe to understand more about temporal lobe seizures. The focus of these two pages is the visual symptoms that are exhibited in both artificial stimulation and temporal lobe seizures. The first page will explain the mechanisms of artificial stimulation, and the next page will focus on experiments that have used the tools described on this page.
TMS
Beyond studying people with
temporal lobe epilepsy, a lot of work has been done studying the effects
of stimulating the temporal lobe artificially. Scientists want
to study what happens when there is extra electrical activity in the
brain, and they want to control where that activity is taking place
One of the main ways that scientists stimulate the brain is called
transcranial magnetic stimulation, or TMS
TMS is a non-invasive experimental technique, which means that it is done with
a machine that is located outside of the body and does not require any
sort of surgery for it to work effectively. TMS works by having
a coil of wire placed near (or on) the scalp and having electricity
flow through it. The electricity forms a magnetic field that painlessly
passes into the head. The magnetic field stimulates an electrical
current in the brain. This current interrupts normal brain functioning
and induces new brain activity (Walsh & Cowey, 2000).
It is possible to control how large the magnetic field is and how much
electricity is generated in the brain. It is also possible to
only stimulate a very specific part of the brain in order to study that
part in particular. For the purpose of this website I will focus
on stimulation of the temporal lobe, but TMS can be used to stimulate
other parts of the brain as well (Wasserman, 1998; Kamitani & Shimojo, 1999;
Hallett, 2000).
TMS is being used in neuroscience
to study many different aspects of brain functioning, from perception
to learning. It is also being explored as a tool for treatment
of certain disorders. An analogy for
TMS is that it creates a "noise" that interrupts neural processes.
It creates random electrical signals that disrupt the organized signals
that are a part of normal functioning. In doing so it prevents
a task from being completed, or it stimulates abnormal sensory responses.
TMS is used to temporarily produce cognitive impairments similar to
impairments that exist in some patients who have TLE. The information gathered
from the normal subjects that undergo TMS is used to understand the
deficits that patients (with brain damage) are experiencing. Artificially
stimulating the temporal lobe allows scientists to understand more about
temporal lobe epilepsy (Walsh &Cowey, 2000). Direct Electrical Stimulation of the Brain Scientists have also studied
the effects of stimulating the brain through electrodes. An electrode is a conductor through which electricity enters (or is measured) in the brain.
Electrodes can be implanted in the brain, and they can be used to stimulate
very specific parts of the brain. This form of artificial stimulation
has been used much longer than TMS. Because the electrode is implanted
directly into the brain it not only affects the neurons near its tip, but it also
Some epilepsy patients have
electrodes implanted in their brain to map their brain waves regularly.
Additionally, electrical stimulation of the brain is sometimes performed during surgery to make sure the surgeon is working in the correct part of the brain.
This electrical stimulation has been shown to produce responses that
are similar to auras. Aura
is a term that describes the experience right before a seizure occurs.
It is the part of the seizure that can be remembered. If certain
regions in the temporal lobe are stimulated, they can produce complex
hallucinations or illusions. Sometimes the experience can seem
more "vivid" than real life. These experiences are often specific
to an individual, and the actual part of the temporal lobe that is stimulated
does not seem to be of great importance with regard to what events are
experienced (Fried, 1997).
Some of the earliest work done
with artificial brain stimulation involved stimulating the surface of
the brain during surgery. Because of this research we have a much
clearer map of the functions of certain parts of the brain. Surface
stimulation was (and still is) done to ensure that if parts of the brain
need to be cut out to fix a problem, the parts removed would not include
areas that perform vital functions. Wilder Penfield did some of
the earliest mapping of the brain, and he was also involved in research
that used stimulation to aid in treatment of temporal lobe epilepsy
(Penfield & Baldwin, 1952).
Not all experiments involve
TMS. A lot of what we know about parts of the brain is understood
because scientists have studied people who have damage to those specific
areas in the brain. Additionally, scientists have studied animals
and their responses to lesions and other damage to certain parts of
the brain (Miyashita, 1993). Experiential PhenomenaOther Mechanisms
Multiple circuits in the brain
process higher-level cognitive functions at the same time. This
partly explains the experiential phenomenon associated with temporal
lobe epilepsy. Experiential phenomena are the hallucinations that
are realistic and associated with the sense that you are experiencing
something. Emotions or memories could be involved. It goes
beyond just a visual hallucination of an object, and it utilizes many
senses to make it feel like the patient is actually experiencing something.
The localized electrical stimulation (either caused by the epilepsy
or artificially) produces effects throughout the brain. It causes
some parts to activate and it causes other parts to stop working, the
combination of which causes hallucinations and illusions (Gloor, 1990).
A number of experiments have
been done and it is pretty clear that perception of objects is directly
related to the temporal lobe in the brain. Experiments have shown
that the temporal lobe is connected to other parts of the brain that
analyze visual information, and it has been shown to play a role in
analysis of that information as well (Miyashita, 1993).