Introduction

1. A. Deep Brain Stimulation (DBS) is a surgical procedure in which a patient suffering Parkinsons has electrodes implanted into certain area(s) of the brain.

B. Commonly thought as a type of pacemaker for the brain (von Bubnoff, 2009), DBS uses a generator as a power supply. Electrodes then stimulate the brain, which prevents many of the Parkinsons disease motor symptoms. DBS reduces tremors, rigidity and it improves mobility (Ostergaard, 2002).

C. DBS is useful for other neurological symptoms, such as, movement disorders, traumatic brain injury, obsessive-compulsive disorder and severe depression (von Bubnoff, 2009).

D.

2. A. The entorhinal cortex is a section in the brain that plays a role in forming memories and in spatial memory. B.

PurposeThe purpose of this experiment is to determine whether or not Deep Brain Stimulation of the entorhinal cortex may affect ones memory performance.

MethodsA. Seven patients who had treatment resistant epilepsy were the subject of this study. Six patients had electrodes implanted in the entorhinal area. Five had at least one electrode implanted in the in the hippocampus, and four patients had electrodes implanted in both the hippocampus and the entorhinal cortex. The electrodes were implanted using MRI guidance and had platinum contacts so an electroencephalograph could measure neural activity.

B. Stimulation for all patients was bipolar, in which the elctrodes were implanted 1.5 mm apart. The implanted pulse generator sends an electric pulse every five seconds. The pulse width was 300 seconds and the current frequency was 50 Hz. The maximum voltage was 3 volts. These parameters are similar seen to help patients suffering from epileptic seizers.

C. To test spatial learning the patients were placed in a virtual reality environment in which the patients had to bring passengers to certain buildings, such as a restaurant. The six who had entorhinal stimulation were tested in one session. Those four who also had hippocampal stimulation were tested in groups. The one subject who had bipolar stimulation of the hippocampus was tested individually. The patient was tested with stimulation of one lobe than was tested with stimulation of the other lobe.

D. In each of the testing session the patients were thought to navigate to six different stores that were present in the virtual reality environment (to note, the virtual reality environment was essentially a game in which patients moved an onscreen character with a joystick). There sessions were sub grouped into four block. In each block the patient would have to revisit each location. In the first three block stimulation was applied to the patients while they tried to navigate to three different stores though stimulation was not applied when the subjects tried to navigate to the other three stores. No stimulation at all was given in the fourth block.

E. The four blocks had 2 minute intervals between them. In this time the patients would be perform control tasks. These tasks were to determine if the results derived were a result of the DBS or a result of the improvement in ones perception or motor abilities.

Quantifying Spatial Learning A. When a patient took a route to travel to a specific place in the virtual reality environment, the length of the route was measured. The difference between the shortest path and this path was then measured. The time taken to travel to a specific place was also taken into consideration.

EEGA. EEG data was taken only for the four patients who had DBS in the entorhinal and the hippocampus. Only electrical frequencies of theta (3 to 8 Hz), alpha (9 to 14 Hz), beta (15 to 35 Hz) and gamma (36 to 100 Hz) were looked at. The EEG waveform was looked at before and during DBS. Statistical AnalysisA. The study analyzed the excess path length taken by the patient and the time taken. Though, with respect to the condition ( stimulation ,and non-stimulation) as well as the block ( blocks one, two , three)

B. The study compared the nonstimulation block (4), with the blocks that involved stimulation (1, 2, and 3). They were compared using the Wilcoxen signed rank test.

C. The Wilcoxen test is a test that compares two subjects and determines whether there is a significant population mean.

D. The results of the Hippocampus stimulation trials were compared with the Entorhinal Region stimulation trials.

E. A Binomial sign test was done to determine whether or no that the patients chose a shorter route by chance.

F. EEG amplitude was also compared. This was done by determining the average amplitude of the waveform before the subject did the spatial memory test .Then this was compared to the wave form after stimulation. The same thing was also done for when a patient did not receive stimulation at all during a block. ResultsA. Patients who received Entorhinal Stimulation showed to have taken shorter routes and have a shorter latency period when stimulation was turned on.

B. Without stimulation the average path length taken for these patients was 64% longer.

C. On the other hand, stimulation of the Hippocampus did not show to have significantly altered the subjects memory performance. Neither the latency period nor the paths taken were shortened.

EEG ResultsA. Looking at the four patients who had Entorhinal and Thalamic deep brain stimulation it was seen that there was an increase in theta rhythm by 44.3% (+/- 6.9) percent

Discussion

A. This study showed that stimulation of the Entorhinal Region may increase ones memory performance.

B. The study also proved that stimulation of the Hippocampus would not improve memory enhancement.

C. Yet, this study contained many problems. The patients within this study all suffered from epilepsy. A disease that can impair ones cognitive function. Thus, it not known for certain if this study can be generalized to everyone.

D. There was also a small study size, which limited significance of smaller findings that the study found.

E. The patients also did not receive prolong stimulation. The maximum time stimulation was turned on was about 14 minutes.

ConclusionA. While it is not certain that results if this study can be generalized to everyone, it is believed that they hold true for those who suffer from mental impairments; such as Alzheimers disease.

B. Future studies may generalize the study sample to those who dont suffer mental impairment.

C. A larger study sample could be used as well. Though, this would be difficult since DBS is quite invasive and costly.

D. Lastly the prolong effect of stimulation of the Entorhinal Area could be looked at. Regardless of the subjects medical history. For this study does not show if these results will be consistent within a year.

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