"Neonics" irreversibly bind to receptors. Normally, the binding is reversible and receptor may be reused. In case of "Neonics" it is not happening and receptors gradually depleted - accumulation effect. It could "accumulate" for decades until any manifestation. I would imagine that "manifestation" would be similar to Alzheimer, dementia. Since "Neonics" are in use for a decade already, it is quite possible that "result" is there, in our brains with little bit less ability to memorize, think, made logical connections... Unfortunately, it is extremely difficult to prove such correlation. Thus, there would be plenty of people, who would deny any effects of "neonics" on them. My personal theory is that it would first affect people in the areas, where "neonics" are widely used (corn belt?). The symptoms may include mental inflexibility, inability to process new information, decline of communicative skills, decline in logical thinking and so on. The problem with this is that such changes would be irreversible, thus, no treatment possible. Also - it is accumulative, negligible amount over long period of time could potentially do a substantial irreversible damage. Note: it is my own interpretation of the available to me scientific data, it is not a fact - do your own research and made your own conclusions! Also - of coarse - nothing personal.