SUMMARY AND CONCLUSIONS

1. To test the mode of functional connectivity in the basal gan-glia circuitry, we studied the activity of simultaneously recorded neurons in the globus pallidus (GP) of a behaving rhesus monkey. The cross-correlograms of pairs of neurons in the GP were com-pared with those of neurons in the thalamus and frontal cortex and to the cross-correlograms of pallidal pairs after 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treatment. 2. In contrast with cortical and thalamic neuronal activity, al-most all pairs (n = 76/81 pairs; 93.8%, 1,629/1,651 histograms; 98.7%) of GP neurons in the normal monkey were not driven by a common input. 3. The monkey was systemically treated with MPTP until the appearance of parkinsonian signs and an intermittent 7- to 1 l-Hz action/postural tremor. After the MPTP treatment, many pallidal neurons (49/140; 35%) became oscillatory, and 19 % (n = 31/ 162) of pallidal pairs had oscillatory cross-correlograms. 4. These results support the model of parallel processing in the basal ganglia of normal monkeys and suggest a breakdown of the independent activity in the parkinsonian state