In the intricate dance of information processing within the human brain, thalamocortical (TC) relay neurons play a pivotal role as they orchestrate the rhythm of communication between the thalamus and the cerebral cortex. As the pace of this communication modulates between slow, bursting patterns and rapid, tonic firing, the energy demands of these neural activities shift in turn. A groundbreaking study published in Scientific Reports investigates the metabolic costs of these temporal firing patterns, providing invaluable insights into the energetic economies of the brain.
DOI: 10.1038/s41598-019-43460-8
Reference: Yi Guosheng and Grill Warren M., “Average firing rate rather than temporal pattern determines metabolic cost of activity in thalamocortical relay neurons”, Scientific Reports, 2019.
Abstract
The brain’s capacity for function relies on the delicate balance of energy consumption and supply. TC relay cells effectively illustrate this balance by operating in two modes – the burst mode, typically associated with sleep or attentional lapses, and the tonic mode, which dominates during active sensory processing. Using a combination of experimental data and simulations, Guosheng and Grill revealed that the average firing rate, rather than the mode of neural activity, predominantly determines the metabolic cost of these neurons.
Introduction
The brain, despite being only 2% of the body’s mass, consumes an estimated 20% of the body’s energy. The study by Guosheng and Grill takes a critical step toward elucidating the underlying metabolic expenses that different firing patterns incur in neural circuitry. While the burst and tonic modes were initially thought to have distinct metabolic signatures, this paper argues that the energy usage of TC relay neurons is, to a larger extent, a function of the overall average firing rate.
Methodology
The authors crafted a biophysically-realistic model of a TC relay neuron to simulate neural activity. They then measured the consequential ion fluxes and converted these to ATP demand – the cellular currency of energy. This method allowed for precise quantification of the metabolic cost across a spectrum of firing rates, shedding light on the relationship between firing patterns and energy utilization.
Results
Guosheng and Grill found that higher average firing rates led to increased metabolic costs, regardless of whether the neuron was in burst or tonic mode. This discovery refines our understanding of neural efficiency and challenges previous theories about the energy expenditure of rhythmic brain activity. Moreover, it underlines the importance of considering the role of firing rate when assessing the brain’s energy budget.
Discussion
The results carry profound implications for scientists studying brain energetics, with applications ranging from the design of neural prosthetics to improved treatments for neurological disorders. The research provides a clearer picture of how the brain’s power supply is harnessed to support cognitive functions and has the potential to inform therapeutic strategies aimed at managing conditions like epilepsy or Parkinson’s where abnormal firing rates are implicated.
Conclusion
This paper marks a significant step forward in our scientific understanding of the metabolic cost associated with neural activity. The insight that the average firing rate is more influential than previously thought suggests that future research should focus on quantifying and modifying firing rates to optimize energy consumption in the brain.
Keywords
1. Neuronal Energy Consumption
2. Thalamocortical Relay Neurons
3. Firing Rate and Metabolism
4. Neural Efficiency
5. ATP Demand in Brain
References
1. Sherman, S. M. (2001). Tonic and burst firing: dual modes of thalamocortical relay. Trends in Neuroscience, 24(2), 122-126. DOI: 10.1016/S0166-2236(00)01714-8
2. Zeldenrust, F., Chameau, P., & Wadman, W. J. (2018). Spike and burst coding in thalamocortical relay cells. PLOS Computational Biology, 14(2), e1005960. DOI: 10.1371/journal.pcbi.1005960
3. Jahnsen, H. & Llinás, R. (1984). Electrophysiological properties of guinea-pig thalamic neurones: an in vitro study. Journal of Physiology, 349, 205–226. DOI: 10.1113/jphysiol.1984.sp015153
4. Guillery, R. W., & Sherman, S. M. (2002). Thalamic relay functions and their role in corticocortical communication: generalizations from the visual system. Neuron, 33(2), 163-175. DOI: 10.1016/S0896-6273(01)00582-7
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In summary, Yi Guosheng and Warren M. Grill’s study delivers crucial insights into the metabolic demands of thalamocortical communications. While these findings highlight the importance of the rate of neuronal firing in energy consumption, future investigations are required to further decode the complex relationship between brain function and its metabolic needs.