A Limit to Learning?: Effects of Plasticity on Brain Energy Utilization

Neural connections can be changed by experience, a property known as neuronal plasticity. Neuronal plasticity is believed to be a key mechanism by which memory and learning occur in the brain. To study potential consequences... [ view full abstract ]

Neural connections can be changed by experience, a property known as neuronal plasticity. Neuronal plasticity is believed to be a key mechanism by which memory and learning occur in the brain. To study potential consequences of plasticity for the brain, we experimentally induced a ubiquitous form of plasticity (Long-term potentiation; LTP) in the perforant pathway of the hippocampus in rat brains by delivering high frequency stimulation through surgically placed electrodes.  Simultaneous measurements of electrically-evoked neuronal responses and relative concentrations of energy metabolites (glucose or lactate) enabled us to assess how LTP affects brain metabolism. We observed striking differences in brain metabolism when comparing responses pre- and post-LTP induction with plasticity, and these charges are associated with an energetic shift towards increased reliance upon glycolytic activity. These findings reflect that the mechanisms of LTP produce costly, and lasting, energetic demands that must be met through alterations in brain metabolism. The results of this research provide insight into the energy constraints imposed on the brain by learning and memory, suggesting that the process of inducing memory formation may be energetically costly and possibly limited. Additionally, this may have important implications for our understanding of neurodegenerative diseases.