Transfer of learned information between ganglia in the insect ventral nerve cord

A yoked control training procedure was used on the decapitated cockroach, L. maderae. The right prothoracic leg was trained to lift in order to avoid a shock. It was found that this information transferred via the two interganglionic connectives from the first or prothoracic ganglion (T1) to the second or mesothoracic ganglion (T2) so that now the right mesothoracic leg lifted to avoid shock even though it was not directly trained. If both connectives were cut before training T1, no transfer to T2 was seen, i.e. the mesothoracic leg did not lift and avoid shock. However, if both connectives were cut immediately after training T1, the information had already transferred and was available for use by T2. There was redundancy in the transfer in that either connective alone could carry the same information from T1 to T2. Either mesothoracic leg could tap into this information. Using a reversible cold block on the connectives, it was found that if it was applied before training T1 it did not interfere with T1 learning but no transfer to T2 was seen after the cold block wore off. That the block was transitory and did not permanently impair the connectives was shown by the fact that if it was applied and then allowed to wear off before training began there was normal learning in T1 and transfer to T2. The transection and cold-block studies were consistent in demonstrating that the transfer of the information was 'on-line' and only occurred during T1 learning. If transfer was blocked during T1 learning the information could not be transferred or tapped into by T2 at a later time even though it was stored in T1 and available for later use by T1. The transfer occurred so quickly it most likely occurred via nerve impulses. Because no primary sensory or motor neurons are in the connectives, the information must have been coded onto interneurones for transfer from the first (T1) to the second (T2) ganglion.