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by: Zimmerman, E. M., Konopka, C. J., Epstein, P. S., & Konopka, L. M.

Relationship Between Thalamic Asymmetry and Right-Hemisphere Theta Abnormalities

Relationship Between Thalamic Asymmetry and Right-Hemisphere Theta Abnormalities

Objective: The right hemisphere of the brain plays a significant role in the experience and expression of emotions and is often deregulated in psychiatric patients. The thalamus influences cortical and subcortical activity in both hemispheres via widespread thalamocortical/cortiocothalamic projections. Asymmetrical thalamic activity may impact function in one hemisphere. In our population of psychiatric patients studied with a combination of positron emission tomography (PET) and quantitative EEG (qEEG), most patients demonstrated reduced metabolic activity in their right thalamus. We hypothesized greater right-sided (R<L) thalamic asymmetry in metabolic activity would significantly correlate with focal EEG abnormalities in the right hemisphere.

Methods: We analyzed archival PET and qEEG data of 48 patients from a community-based psychiatric outpatient clinic. Patients presented with a variety of symptoms, often with complex and comorbid diagnoses. Statistical evaluation for PET images was obtained with BRASS software (HERMES software, total count adjustment). Significant focal EEG abnormalities were identified using low-resolution brain electromagnetic tomography (LORETA). Significance was set at ±2 standard deviations. Independent t-tests (p<0.05) were utilized to compare percent differences between right and left thalamic count/voxel ratios as well as normalized asymmetry z-scores between patients with focal EEG abnormalities in the right hemisphere and those without.

Results: Thirty-five (n=35) patients demonstrated decreased activity in the right thalamus as compared to the left. Of these patients, twelve (n=12) demonstrated one or more right-hemispheric focal EEG abnormalities in theta (.) frequencies and twenty-three (n=23) did not have any right-sided focal . findings. A significant difference was found in percent difference of right/left metabolic activity between patients with right focal . abnormalities (M=8.90, SD=4.92) and those without (M=5.36, SD=4.07); t = -2.268, p = 0.030. There was also a significant difference in normalized asymmetry z-scores for patients with right focal . abnormalities (M=3.31, SD=1.49) and those without (M=2.00, SD=1.38); t = -2.590, p = 0.014.

Conclusions: The findings support the hypothesis in that right-sided thalamic asymmetry is correlated to presence of right-hemispheric focal . abnormalities in EEG. The results offer implications for relationships between thalamic function and electrophysiological activity. This study supports a multimodality approach combining nuclear imaging and EEG to enhance identification of abnormal function in psychiatric patients.

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