After the huge reduction in number of neurons between the cortex and the striatum (see corticostriate connection), the striatopallido-nigral connection is a further reduction in the number of transmitting compared to receiving neurons. Numbers indicate that, for 31 million striatal spiny neurons in macaques, there are only 166000 lateral pallidal neurons, 63000 medial pallidal, 18000 lateral nigral and 35000 in the pars reticulata. If the number of striatal neurons is divided by their total number, as an average, each target neuron may receive information from 117 striatal neurons. (Numbers in man lead to about the same ratio). A different approach starts from the mean surface of the pallidonigral target neurons and the number of synapses that they may receive. Each pallidonigral neuron may receive 70000 synapses. Each striatal neuron may contribute 680 synapses. This leads again to an approximation of 100 striatal neurons for one target neuron. This represents a huge, infrequent, reduction in neuronal connections. The consecutive compression of maps cannot preserve finely distributed maps (as in the case for instance of sensory systems). The fact that a strong anatomical possibility of convergence exists does not means that this is constantly used. A recent modeling study starting from entirely 3-d reconstructed pallidal neurons showed that their morphology alone is able to create a center-surround pattern of activity. Physiological analyses have shown a central inhibition/peripheral excitation pattern, able of focusing the pallidal response in normal conditions. Percheron and Filion (1991) thus argued for a "dynamically focused convergence". Disease, is able to alter the normal focusing. In monkeys intoxicated by MPTP, striatal stimulations lead to a large convergence on pallidal neurons and a less precise mapping.