@article{pmid40438628,

title = {Polysemia as a concept to understand the encoding of sensory information},

author = {Christian Ethier and Zohreh Vaziri and Martin Deschênes},

doi = {10.3389/fnins.2025.1588437},

issn = {1662-4548},

year  = {2025},

date = {2025-01-01},

journal = {Front Neurosci},

volume = {19},

pages = {1588437},

abstract = {In this article, we explore the concept of polysemia in sensory information processing within the brain. We suggest that, just as words can have different meanings based on context, sensory inputs are interpreted differently depending on the animal's current state and behavior. Focusing on the trigeminal sensory nuclei in rats, we highlight the role of inhibitory circuits in gating sensory information and propose that sensory signals are polysemic, with their meaning influenced by emotional, hormonal, and motivational factors.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{pmid37400255,

title = {Interchangeable Role of Motor Cortex and Reafference for the Stable Execution of an Orofacial Action},

author = {Michaël A Elbaz and Maxime Demers and David Kleinfeld and Christian Ethier and Martin Deschênes},

doi = {10.1523/JNEUROSCI.2089-22.2023},

issn = {1529-2401},

year  = {2023},

date = {2023-07-01},

journal = {J Neurosci},

volume = {43},

number = {30},

pages = {5521--5536},

abstract = {Animals interact with their environment through mechanically active, mobile sensors. The efficient use of these sensory organs implies the ability to track their position; otherwise, perceptual stability or prehension would be profoundly impeded. The nervous system may keep track of the position of a sensorimotor organ via two complementary feedback mechanisms-peripheral reafference (external, sensory feedback) and efference copy (internal feedback). Yet, the potential contributions of these mechanisms remain largely unexplored. By training male rats to place one of their vibrissae within a predetermined angular range without contact, a task that depends on knowledge of vibrissa position relative to their face, we found that peripheral reafference is not required. The presence of motor cortex is not required either, except in the absence of peripheral reafference to maintain motor stability. Finally, the red nucleus, which receives descending inputs from motor cortex and cerebellum and projects to facial motoneurons, is critically involved in the execution of the vibrissa positioning task. All told, our results point toward the existence of an internal model that requires either peripheral reafference or motor cortex to optimally drive voluntary motion. How does an animal know where a mechanically active, mobile sensor lies relative to its body? We address this basic question in sensorimotor integration using the motion of the vibrissae in rats. We show that rats can learn to reliably position their vibrissae in the absence of sensory feedback or in the absence of motor cortex. Yet, when both sensory feedback and motor cortex are absent, motor precision is degraded. This suggests the existence of an internal model able to operate in closed- and open-loop modes, requiring either motor cortex or sensory feedback to maintain motor stability.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{pmid35087926,

title = {Assessment of Corticospinal Excitability in Awake Rodents Using EMG-Controlled Intracortical Stimulation},

author = {Windsor K C Ting and Derek Burns and Maxime Huot-Lavoie and Christian Ethier},

doi = {10.21769/BioProtoc.4267},

issn = {2331-8325},

year  = {2021},

date = {2021-12-01},

journal = {Bio Protoc},

volume = {11},

number = {24},

pages = {e4267},

abstract = {Assessment of corticospinal excitability (CSE) is an essential component of experiments designed to induce or study neuronal plasticity in the motor system. Common examples are paired associative stimulation (PAS), theta-burst stimulation (TBS), intensive motor training, or any methods aimed at potentiating the corticomotor system in the hope of promoting better recovery after neurological insult. To date, rodent models of CSE assessment have mostly been completed under anaesthesia, which greatly affects the level of CSE, as well as the mechanisms of plasticity. Experiments in awake animals are difficult because the ongoing state of behavior affects the excitability of the motor system and complicates the assessment of CSE. To address this issue, we have designed a novel approach for CSE assessment in awake behaving rodents, enabling a reliable measure of evoked motor responses obtained from cortical microstimulation in repeatable conditions of ongoing motor activity. The system relies on chronically implanted intracortical and intramuscular electrodes and a custom-made software control system, enabling the user to require that precise parameters of EMG activity be met before cortical stimulation probes are delivered. This approach could be used for further studies of PAS, TBS or other interventions requiring the assessment of CSE under repeatable conditions. We provide fabrication schematics and a list of materials for the implant, as well as instructions for running a custom-made MATLAB codebase, customizing the PAS protocol, and performing the complete analysis of experimental data. We hope these tools can further facilitate animal research in the field of neuroplasticity and neurorehabilitation.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{pmid34054410,

title = {Neurostimulation for Stroke Rehabilitation},

author = {Windsor Kwan-Chun Ting and Faïza Abdou-Rahaman Fadul and Shirley Fecteau and Christian Ethier},

doi = {10.3389/fnins.2021.649459},

issn = {1662-4548},

year  = {2021},

date = {2021-01-01},

journal = {Front Neurosci},

volume = {15},

pages = {649459},

abstract = {Neurological injuries such as strokes can lead to important loss in motor function. Thanks to neuronal plasticity, some of the lost functionality may be recovered over time. However, the recovery process is often slow and incomplete, despite the most effective conventional rehabilitation therapies. As we improve our understanding of the rules governing activity-dependent plasticity, neuromodulation interventions are being developed to harness neural plasticity to achieve faster and more complete recovery. Here, we review the principles underlying stimulation-driven plasticity as well as the most commonly used stimulation techniques and approaches. We argue that increased spatiotemporal precision is an important factor to improve the efficacy of neurostimulation and drive a more useful neuronal reorganization. Consequently, closed-loop systems and optogenetic stimulation hold theoretical promise as interventions to promote brain repair after stroke.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{pmid34504415,

title = {A Wireless Electro-Optic Platform for Multimodal Electrophysiology and Optogenetics in Freely Moving Rodents},

author = {Guillaume Bilodeau and Gabriel Gagnon-Turcotte and Léonard L Gagnon and Iason Keramidis and Igor Timofeev and Yves De Koninck and Christian Ethier and Benoit Gosselin},

doi = {10.3389/fnins.2021.718478},

issn = {1662-4548},

year  = {2021},

date = {2021-01-01},

journal = {Front Neurosci},

volume = {15},

pages = {718478},

abstract = {This paper presents the design and the utilization of a wireless electro-optic platform to perform simultaneous multimodal electrophysiological recordings and optogenetic stimulation in freely moving rodents. The developed system can capture neural action potentials (AP), local field potentials (LFP) and electromyography (EMG) signals with up to 32 channels in parallel while providing four optical stimulation channels. The platform is using commercial off-the-shelf components (COTS) and a low-power digital field-programmable gate array (FPGA), to perform digital signal processing to digitally separate in real time the AP, LFP and EMG while performing signal detection and compression for mitigating wireless bandwidth and power consumption limitations. The different signal modalities collected on the 32 channels are time-multiplexed into a single data stream to decrease power consumption and optimize resource utilization. The data reduction strategy is based on signal processing and real-time data compression. Digital filtering, signal detection, and wavelet data compression are used inside the platform to separate the different electrophysiological signal modalities, namely the local field potentials (1-500 Hz), EMG (30-500 Hz), and the action potentials (300-5,000 Hz) and perform data reduction before transmitting the data. The platform achieves a measured data reduction ratio of 7.77 (for a firing rate of 50 AP/second) and weights 4.7 g with a 100-mAh battery, an on/off switch and a protective plastic enclosure. To validate the performance of the platform, we measured distinct electrophysiology signals and performed optogenetics stimulation  in freely moving rondents. We recorded AP and LFP signals with the platform using a 16-microelectrode array implanted in the primary motor cortex of a Long Evans rat, both in anesthetized and freely moving conditions. EMG responses to optogenetic Channelrhodopsin-2 induced activation of motor cortex  optical fiber were also recorded in freely moving rodents.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{pmid32139377,

title = {Paired Associative Stimulation Fails to Induce Plasticity in Freely Behaving Intact Rats},

author = {Windsor Kwan-Chun Ting and Maxime Huot-Lavoie and Christian Ethier},

doi = {10.1523/ENEURO.0396-19.2020},

issn = {2373-2822},

year  = {2020},

date = {2020-01-01},

journal = {eNeuro},

volume = {7},

number = {2},

abstract = {Paired associative stimulation (PAS) has been explored in humans as a noninvasive tool to drive plasticity and promote recovery after neurologic insult. A more thorough understanding of PAS-induced plasticity is needed to fully harness it as a clinical tool. Here, we tested the efficacy of PAS with multiple interstimulus intervals in an awake rat model to study the principles of associative plasticity. Using chronically implanted electrodes in motor cortex and forelimb, we explored PAS parameters to effectively drive plasticity. We assessed changes in corticomotor excitability using a closed-loop, EMG-controlled cortical stimulation paradigm. We tested 11 PAS intervals, chosen to force the coincidence of neuronal activity in the motor cortex and spinal cord of rats with timings relevant to the principles of Hebbian spike timing-dependent plasticity. However, despite a relatively large number of stimulus pairings (300), none of the tested intervals reliably changed corticospinal excitability relative to control conditions. Our results question PAS effectiveness under these conditions.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{pmid31352352,

title = {A Wireless Electro-Optic Headstage With a 0.13- μm CMOS Custom Integrated DWT Neural Signal Decoder for Closed-Loop Optogenetics},

author = {Gabriel Gagnon-Turcotte and Iason Keramidis and Christian Ethier and Yves De Koninck and Benoit Gosselin},

doi = {10.1109/TBCAS.2019.2930498},

issn = {1940-9990},

year  = {2019},

date = {2019-10-01},

journal = {IEEE Trans Biomed Circuits Syst},

volume = {13},

number = {5},

pages = {1036--1051},

abstract = {We present a wireless electro-optic headstage that uses a 0.13- μm CMOS custom integrated circuit (IC) implementing a digital neural decoder (ND-IC) for enabling real-time closed-loop (CL) optogenetics. The ND-IC processes the neural activity data using three digital cores: 1) the detector core detects and extracts the action potential (AP) of individual neurons by using an adaptive threshold; 2) the data compression core compresses the detected AP by using an efficient Symmlet-2 discrete wavelet transform (DWT) processor for decreasing the amount of data to be transmitted by the low-power wireless link; and 3) the classification core sorts the compressed AP into separated clusters on the fly according to their wave shapes. The ND-IC encompasses several innovations: 1) the compression core decreases the complexity from O(n ) to O(n · log(n)) compared to the previous solutions, while using two times less memory, thanks to the use of a new coefficient sorting tree; and 2) the AP classification core reuses both the compressed DWT coefficients to perform implicit dimensionality reduction, which allows for performing intensive signal processing on-chip, while increasing power and hardware efficiency. This core also reuses the signal standard deviation already computed by the AP detector core as threshold for performing automatic AP sorting. The headstage also introduces innovations by enabling a new wireless CL scheme between the neural data acquisition module and the optical stimulator. Our CL scheme uses the AP sorting and timing information produced by the ND-IC for detecting complex firing patterns within the brain. The headstage is also smaller (1.13 cm ), lighter (3.0 g with a 40 mAh battery) and less invasive than the previous solutions, while providing a measured autonomy of 2h40, with the ND-IC. The whole system and the ND-IC are first validated in vivo in the LD thalamus of a Long-Evans rat, and then in freely-moving CL experiments involving a mouse virally expressing ChR2-mCherry in inhibitory neurons of the prelimbic cortex, and the results show that our system works well within an in vivo experimental setting with a freely moving mouse.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{pmid31507526,

title = {Impaired Motor Learning Following a Pain Episode in Intact Rats},

author = {Maxime Huot-Lavoie and Windsor Kwan-Chun Ting and Maxime Demers and Catherine Mercier and Christian Ethier},

doi = {10.3389/fneur.2019.00927},

issn = {1664-2295},

year  = {2019},

date = {2019-01-01},

journal = {Front Neurol},

volume = {10},

pages = {927},

abstract = {Motor learning and pain are important factors influencing rehabilitation. Despite being mostly studied independently from each other, important interactions exist between them in the context of spinal cord injury, whether to the spinal cord or the body. Ongoing or recent past episodes of nociceptive activity can prevent motor learning in spinalized rats. In intact animals, it has been proposed that supraspinal activity could counter the repressive effect of nociception on motor system plasticity, but this has not yet been verified in behavioral conditions. The aim of this study was to test whether a recent episode of nociception affects subsequent motor learning in intact animals. We trained rodents to walk on a custom-made horizontal ladder. After initial training, the rats underwent a week-long rest, during which they were randomly assigned to a control group, or one out of two pain conditions. Nociceptive stimuli of different durations were induced through capsaicin or Complete Freund's Adjuvant injections and timed so that the mechanical hypersensitivity had entirely subsided by the end of the resting period. Training then resumed on a modified version of the horizontal ladder. We evaluated the animals' ability to adapt to the modified task by measuring their transit time and paw misplacements over 4 days. Our results show that prior pain episodes do affect motor learning in neurologically intact rats. Motor learning deficits also seem to be influenced by the duration of the pain episode. Rats receiving a subcutaneous injection of capsaicin displayed immediate signs of mechanical hypersensitivity, which subsided rapidly. Nonetheless, they still showed learning deficits 24 h after injection. Rats who received a Complete Freund's Adjuvant injection displayed mechanical hypersensitivity for up to 7 days during the resting period. When trained on the modified ladder task upon returning to normal sensitivity levels, these rats exhibited more prolonged motor learning deficits, extending over 3 days. Our results suggest that prior pain episodes can negatively influence motor learning, and that the duration of the impairment relates to the duration of the pain episode. Our results highlight the importance of addressing pain together with motor training after injury.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{pmid30315158,

title = {Cortical population activity within a preserved neural manifold underlies multiple motor behaviors},

author = {Juan A Gallego and Matthew G Perich and Stephanie N Naufel and Christian Ethier and Sara A Solla and Lee E Miller},

doi = {10.1038/s41467-018-06560-z},

issn = {2041-1723},

year  = {2018},

date = {2018-10-01},

journal = {Nat Commun},

volume = {9},

number = {1},

pages = {4233},

abstract = {Populations of cortical neurons flexibly perform different functions; for the primary motor cortex (M1) this means a rich repertoire of motor behaviors. We investigate the flexibility of M1 movement control by analyzing neural population activity during a variety of skilled wrist and reach-to-grasp tasks. We compare across tasks the neural modes that capture dominant neural covariance patterns during each task. While each task requires different patterns of muscle and single unit activity, we find unexpected similarities at the neural population level: the structure and activity of the neural modes is largely preserved across tasks. Furthermore, we find two sets of neural modes with task-independent activity that capture, respectively, generic temporal features of the set of tasks and a task-independent mapping onto muscle activity. This system of flexibly combined, well-preserved neural modes may underlie the ability of M1 to learn and generate a wide-ranging behavioral repertoire.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{pmid28825407,

title = {Evaluation of high-density, multi-contact nerve cuffs for activation of grasp muscles in monkeys},

author = {N A Brill and S N Naufel and K Polasek and C Ethier and J Cheesborough and S Agnew and L E Miller and D J Tyler},

doi = {10.1088/1741-2552/aa8735},

issn = {1741-2552},

year  = {2018},

date = {2018-06-01},

journal = {J Neural Eng},

volume = {15},

number = {3},

pages = {036003},

abstract = {OBJECTIVE: The objective of this work was to evaluate whether nerve cuffs can selectively activate hand muscles for functional electrical stimulation (FES). FES typically involves identifying and implanting electrodes in many individual muscles, but nerve cuffs only require implantation at a single site around the nerve. This method is surgically more attractive. Nerve cuffs may also more effectively stimulate intrinsic hand muscles, which are difficult to implant and stimulate without spillover to adjacent muscles.nnAPPROACH: To evaluate its ability to selectively activate muscles, we implanted and tested the flat interface nerve electrode (FINE), which is designed to selectively stimulate peripheral nerves that innervate multiple muscles (Tyler and Durand 2002 IEEE Trans. Neural Syst. Rehabil. Eng. 10 294-303). We implanted FINEs on the nerves and bipolar intramuscular wires for recording compound muscle action potentials (CMAPs) from up to 20 muscles in each arm of six monkeys. We then collected recruitment curves while the animals were anesthetized.nnMAIN RESULT: A single FINE implanted on an upper extremity nerve in the monkey can selectively activate muscles or small groups of muscles to produce multiple, independent hand functions.nnSIGNIFICANCE: FINE cuffs can serve as a viable supplement to intramuscular electrodes in FES systems, where they can better activate intrinsic and extrinsic muscles with lower currents and less extensive surgery.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}