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

Lobes of the Brain
A TMS Machine. Image from http://www.princeton.edu

     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

Electrodes in Brain
Electrodes in brain. Image courtesy of http://www.neurosurgeon.org/
affects neurons that come in to the area as well as the passageways that happen to also be in that area. The electrode (when turned on by a doctor or scientist) sends out an electrical signal. This signal affects the surrounding area. Scientists can control the type of electrical signal that is used, and in doing so they can control the effects of the stimulation (McIntyre, Savasta, Walter, & Vitek, 2004). Scientists are also working to make specific electrodes that can more effectively activate specific parts of the brain. They not only change the electrical signal, but they also change the shape of the electrode and the specific points where they implant it in the brain (Buston & McIntyre, 2006).
 

     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).

Other Mechanisms

     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 Phenomena

Electrodes in Brain
Electrodes in brain. Image courtesy of http://www.neurosurgeon.org/

     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). 

 

Religion and Art  • Actual Experiments (And What They Have Found)