Locomotion towards a goal alters the synchronous firing of neurons recorded simultaneously in the subiculum and nucleus accumbens of rats

Rats were implanted with recording electrodes aimed at the subiculum and nu cleus accumbens. They were subsequently placed in a cylindrical environment , where they searched for locations where they would receive rewarding medi al forebrain bundle stimulation. At times a tone was sounded, indicating th at the reward location was in the center of the environment. Animals quickl y learned to switch from random running to goal directed locomotion when th e tone was on. To quantify the synchronous firing between simultaneously re corded neurons in the subiculum and nucleus accumbens, a gravitational clus tering algorithm was employed. Individual neurons were modeled as particles in N dimensional space. Every spike discharge of the neuron augmented the 'gravitational charge' on its model particle. Synchronous firing between tw o cells caused their corresponding particles to draw together over time, du e to the concurrent appearance of gravitational charge. All pair-wise combi nations of cells isolated in subiculum and nucleus accumbens were examined using this algorithm. The firing of nine out of 52 subicular-accumbens cell pairings was significantly more synchronous when the tone was on, and the rat was running towards the central goal. This was also seen for 15 out of 22 subicular-subicular cell pairings. Conversely, only two out of 51 accumb ens-accumbens pairings displayed significant tone dependent changes in sync hronous firing. Thus, synchronous interactions between subiculum and nucleu s accumbens occur preferentially when the animal is required to locate a fi xed goal in space, i.e., the functional connectivity is altered by the navi gational demands of the spatial reward task. (C) 2001 Elsevier Science B.V. All rights reserved.