Abstract
Many motor responses to sensory input, like locomotion or eye movements, are much slower than reflexes. Can simpler animals provide fundamental answers about the cellular mechanisms for motor decisions? Can we observe the 'accumulation' of excitation to threshold proposed to underlie decision making elsewhere? We explore how somatosensory touch stimulation leads to the decision to swim in hatchling Xenopus tadpoles. Delays measured to swimming in behaving and immobilized tadpoles are long and variable. Activity in their extensively studied sensory and sensory pathway neurons is too short-lived to explain these response delays. Instead, whole-cell recordings from the hindbrain reticulospinal neurons that drive swimming show these receive prolonged, variable synaptic excitation lasting for nearly a second following a brief stimulus. They fire and initiate swimming when this excitation reaches threshold. Analysis of the summation of excitation requires us to propose extended firing in currently undefined presynaptic hindbrain neurons. Simple models show that a small excitatory recurrent-network inserted in the sensory pathway can mimic this process. We suggest that such a network may generate slow, variable summation of excitation to threshold. This excitation provides a simple memory of the sensory stimulus. It allows temporal and spatial integration of sensory inputs and explains the long, variable delays to swimming. The process resembles the 'accumulation' of excitation proposed for cortical circuits in mammals. We conclude that fundamental elements of sensory memory and decision making are present in the brainstem at a surprisingly early stage in development. This article is protected by copyright. All rights reserved.
DOI
10.1113/JP276356
Publication Date
2018-08-03
Publication Title
The Journal of Physiology
Publisher
Wiley
ISSN
1469-7793
Embargo Period
2024-11-22
Additional Links
https://www.ncbi.nlm.nih.gov/pubmed/30074236
Keywords
Xenopus laevis, decision-making, locomotion, reticulospinal neurons, somatosensory
Recommended Citation
Koutsikou, S., Merrison-Hort, R., Buhl, E., Ferrario, A., & et al. (2018) 'A simple decision to move in response to touch reveals basic sensory memory and mechanisms for variable response times.', The Journal of Physiology, . Wiley: Available at: https://doi.org/10.1113/JP276356
