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The neuronal network involved in a precise type of calculation procedure, mental subtraction, was investigated by means of functional magnetic resonance imaging. Two tasks were used requiring covert production of numbers: (1) with calculation; (2) without calculation. During the first task, activation was observed in the left dorsolateral prefrontal and premotor cortices, in Broca's area and bilaterally in the inferior parietal cortex. During the second task, activation was mainly observed in Broca's area and to a less extent in the left prefrontal and premotor cortices. Statistical comparison of data in the two situations revealed that the procedure of mental subtraction is mediated by a distributed system which includes predominantly the left dorsolateral prefrontal cortex and the inferior parietal cortex bilaterally.

)werful inhibitions of dorsal horn neurons are triggered in animals by noxious stimulation of large cutaneous areas. This tenomenon described as “Diffuse Noxious Inhibitory Controls” (DNIC) involves supraspinal structures and can be observed, beit indirectly, in man. The question arises as to whether cortical network can be modified by the involvement of DNIC. The asent study was designed to examine the central effects of noxious heat applied to large areas, namely 560 (one hand) or 1120 n2 (two hands) using WRI.