Meeting Abstract
Nervous systems, neurons and neural circuits are under selective pressure to produce behaviour adapted to an animal’s environment but are also subject to energy costs. These costs are dominated by electrical signals because of the need to maintain ionic concentration gradients in neurons. Consequently, voltage-gated conductances that permit ion flow across the neural membrane are well placed to adjust ion flux and influence the energy consumption of signal processing, though their precise role is unclear. Fly R1-6 photoreceptors have been a key system for studying the trade-offs between cost and performance in single neurons; a Law of Diminishing Returns relates performance to cost so that improving performance requires ever larger increases in cost. The photoreceptors of different fly species contain different sets of voltage-gated conductances with different biophysical properties that are related to their visual ecology. Blowfly photoreceptors contain two voltage-gated K+ conductances, a fast and a slow delayed rectifier (DR). By modelling these photoreceptors, we show that the DRs reduce photoreceptor resistance and produce negative feedback that reduces membrane impedance below a specific frequency determined by activation kinetics. The negative feedback from DRs decreases gain and increases bandwidth. In doing so, the DRs do not incur the energy cost of decreasing the resistance of a passive RC membrane. In doing so, they save energy and improve energy efficiency. The DRs create a low bandwidth, low cost regime at low light intensities, and a high bandwidth, high cost regime at high light intensities, enabling blowfly photoreceptors to match energy investment in bandwidth to signal quality. Thus, voltage-gated K+ conductances permit differential energy investment, improving energy efficiency with widespread implications for neuronal function and evolution.
