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The Relationship between Blood Oxygenation Level Dependent Signal and Local Field Potential in the Rat Somatosensory Cortex

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My poster is entitled "The Relationship between Blood Oxygenation Level Dependent Signal and Local Field Potential in the Rat Somatosensory Cortex."

The experiment was divided into two parts: one using Blood Oxygenation Level Dependent (BOLD) Functional Magnetic Resonance Imaging (fMRI) and the other using Local Field Potential (LFP) recording. In each set of experiments, we stimulated the forepaw of a rat and measured the neuronal response in the somatosensory cortex using either fMRI or LFP recording. By comparing the results obtained through the two experiments, we hoped to determine whether fMRI and LFP produce a similar measurement of neuronal activity. We expected both the BOLD response and the LFP response to increase in a similar manner as stimulation intensity increased.

As we performed each experiment, we increased the intensity of the stimulation given to the forepaw of the rat. When we observed the results from each experiment, we hoped to determine how the neuronal response changed as the stimulation intensity increased. When we analyzed the results from the fMRI, we found that the response increased significantly between a stimulus of 1.5 mA and 2 mA although it did not increase between a stimulus of 1 mA and 1.5 mA. When we analyzed our results from LFP recording, on the other hand, neuronal response increased linearly. When we plotted a linear regression to compare stimulation intensity with the average LFP response in Lamina V (1250 µm) of the somatosensory cortex, the LFP data revealed a strong linear correlation with an r2 value of 0.99943. Statistical tests on the data, however, revealed the differences between the LFP responses to different stimuli to be statistically insignificant.

Hopefully, we will achieve better results after we modify and repeat the experiments. For example, we used only four rats for LFP and four rats for fMRI. We noticed during our LFP recordings that the baseline LFP recording was atypical in one of our rats, and the response to stimulation in this rat was very poor. The data from this rat greatly increased the variability of our data. By using a larger number of rats in the future, we believe we will be able to produce more consistent results.

Finally, we hope to run an experiment using a 0mA (or negligible) stimulus to obtain both BOLD and LFP data. We saw an interesting pattern in the BOLD data: the BOLD responses to the 1 mA and the 1.5 mA stimuli were both approximately half of the response to the 2 mA stimulus. The LFP data, on the other hand, increased in a linear progression. We hope that by adding another stimulus intensity to the experiment, we will be able to explain this discrepancy among our results.

Last updated November 16, 2007