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The Journal of Neuroscience, May 15, 2003, 23(10):4012-4016
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BRIEF COMMUNICATION
Functional Correlations between Neighboring Neurons in the Primate Globus Pallidus Are Weak or Nonexistent
Izhar Bar-Gad,1,4 Gali Heimer,4 Ya'acov Ritov,1,2 andHagai Bergman1,3,4 1Center for Neural Computation, 2Department of Statistics, 3Eric Roland Center for Neurodegenerative Diseases, The Hebrew University, Jerusalem 91120, Israel, and 4Department of Physiology, The Hebrew University–Hadassah Medical School, Jerusalem 91120, Israel
The anatomical structure of the basal ganglia displays topographical organization and massive funneling of neuronal projections toward the globus pallidus as well as an axonal collateral system within this nucleus. This structure suggests the formation of correlations between the spiking activities of pallidal cells. Nevertheless, previous studies of remote neurons in the pallidum have reported uncorrelated spiking activity. These correlation results may be challenged, because remote pallidal neurons may be located in different pallidal territories. To further test the independence of pallidal activity, we studied the spiking activity of neighboring pairs recorded by the same electrodes. A narrow peak dominated the correlations of all pairs of neurons recorded on the same electrode. This type of peak is classically interpreted as a sign of strong common input. However, recent mathematical analysis shows that such peaks may derive from a technical inability to detect overlapping spikes by spike-sorting techniques. A long-term shallow trough in the correlation of neighboring neurons may also result from the same effect, which we have termed the "shadowing effect." A comparison of the expected shadowing effect with the actual correlations suggests that no real correlations exist between 93.9% of neighboring pallidal pairs. The remaining 6.1% of the pairs display symmetric long-term positive correlations centered on time 0. Thus, functional interactions between neighboring pallidal neurons do not display any significant differences from the interactions between physically remote neurons in this brain area. Moreover, the combination of anatomical data and current physiological results suggests an active decorrelating process performed in the basal ganglia.
Key words: basal ganglia; cross-correlogram; asynchrony; spike sorting; firing pattern; pallidum; primate
Received Jan. 2, 2003; revised Feb. 25, 2003; accepted Mar. 4, 2003.
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