A STRUCTURAL BASIS FOR MEMORY STORAGE IN MAMMALS

It is proposed that altered dendrite length and de novo formation of n ew dendrite branches in cholinoceptive cells are responsible for long- term memory storage, a process enabled by the degradation of microtubu le-associated protein-2. These memories are encoded as modality-specif ic associable representations. Accordingly, associable representations are confined to cytoarchitectonic modules of the cerebral cortex, hip pocampus, and amygdala. The proposed sequence of events leading to lon g-term storage in cholinoceptive dendrites begins with changes in neur onal activity, then in neurotrophin release, followed by enhanced acet ylcholine release, muscarinic response, calcium influx, degradation of microtubule-associated protein-2, and finally new dendrite structure. Hypothetically, each associable representation consists of altered de ndrite segments from approximately 5000-15000 cholinoceptive cells con tained within one or a few module(s). Simultaneous restructuring durin g consolidation of long-term memory is hypothesized to result in a sim ilar infrastructure among dendrite sets, facilitating co-activation of those dendrite sets by neurotransmitters such as acetylcholine; and c onceivably enabling high energy interactions between those dendrites b y phenomena such as quantum optical coherence. Based on the specific a rchitecture proposed, it is estimated that the human telencephalon con tains enough dendrites to encode 50 million associable representations in a lifetime, or put another way, to encode one new associable repre sentation each minute. The implications that this proposal has regardi ng treatments For Alzheimer's disease are also discussed. (C) 1998 Els evier Science Ltd. Ail rights reserved.