The food reaching test: a sensitive test of behavioral improvements by deep brain stimulation in MPTP-treated monkey

We modified an objective behavioral test, namely the food reaching test (FRT), for quantitative assessment of motor performance improved by deep brain stimulation (DBS) of the subthalamic nucleus (STN) in the Parkinsonian monkeys. The symptomatic features and their severity in 3 monkeys treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) were evaluated with a subjective monkey Parkinson's disease rating scale (PDRS). We then performed STN-DBS with the minimum current intensity that stopped the tremor. The time required for the monkeys to pick up all 5 pieces of potato (FRT time) was measured as a major index to evaluate bradykinesia. The success rate was adopted as another index for assessing overall motor impairments. Although both FRT time and PDRS score were similarly improved by STN-DBS, change of FRT time appeared more sensitive than that of PDRS scores. FRT is an easily trained behavioral test with high objectivity and sensitivity that can be applied for assessing motor performance in MPTP-treated monkeys during experiments in a restrained condition such as functional imaging of the brain.