Journal of Neurophysiology

Berger, Denise J.; Masciullo, Marcella; Molinari, Marco; Lacquaniti, Francesco; d’Avella, Andrea

doi: 10.1152/jn.00657.2018pmid: 32159425

In recent studies, the decomposition of muscle activity patterns has revealed a modular organization of the motor commands. We show, for the first time, that muscle patterns of subjects with cerebellar damage share with healthy controls spatial, but not temporal and spatiotemporal, modules. Moreover, changes in spatiotemporal organization characterize the severity of the subject’s impairment. These results suggest that the cerebellum has a specific role in shaping the spatiotemporal organization of the muscle patterns.

Heid, C.; Mouraux, A.; Treede, R.-D.; Schuh-Hofer, S.; Rupp, A.; Baumgärtner, U.

doi: 10.1152/jn.00444.2019pmid: 32208893

Gamma-band oscillations show hand-foot somatotopy compatible with generation in primary sensorimotor cortex and are present following nociceptive but not tactile stimulation of the hand and foot in humans.

Ariani, Giacomo; Kwon, Young Han; Diedrichsen, Jörn

doi: 10.1152/jn.00054.2020pmid: 32208910

Even for overlearned motor skills such as reaching, movement repetition improves performance. How brain processes associated with motor planning or execution benefit from repetition, however, remains unclear. We report the novel finding of repetition effects for sequential movements. Our results show that repetition benefits are tied to improved online planning of upcoming sequence elements. We also highlight how actual movement experience appears to be more beneficial than mental rehearsal for observing short-term repetition effects.

Colzato, Lorenza; Beste, Christian

doi: 10.1152/jn.00057.2020pmid: 32208895

Brain stimulation approaches are important to gain causal mechanistic insights into the relevance of functional brain regions and/or neurophysiological systems for human cognitive functions. In recent years, transcutaneous vagus nerve stimulation (tVNS) has attracted considerable popularity. It is a noninvasive brain stimulation technique based on the stimulation of the vagus nerve. The stimulation of this nerve activates subcortical nuclei, such as the locus coeruleus and the nucleus of the solitary tract, and from there, the activation propagates to the cortex. Since tVNS is a novel stimulation technique, this literature review outlines a brief historical background of tVNS, before detailing underlying neurophysiological mechanisms of action, stimulation parameters, cognitive effects of tVNS on healthy humans, and, lastly, current challenges and future directions of tVNS research in cognitive functions. Although more research is needed, we conclude that tVNS, by increasing norepineprine (NE) and gamma-aminobutyric acid (GABA) levels, affects NE- and GABA-related cognitive performance. The review provides detailed background information how to use tVNS as a neuromodulatory tool in cognitive neuroscience and outlines important future leads of research on tVNS.

Tomita, Yosuke; Turpin, Nicolas A.; Piscitelli, Daniele; Feldman, Anatol G.; Levin, Mindy F.

doi: 10.1152/jn.00729.2019pmid: 32233891

Reaching from standing requires simultaneous adjustments of end point and center-of-mass (COM) positions. We used uncontrolled manifold analysis to investigate the impact of stroke on the ability to use kinematic redundancy in this task. Our results showed that COM position was stabilized, whereas end-point trajectory was more variable in stroke than healthy subjects. Enhancing the capacity to meet multiple task goals may be beneficial for motor recovery after stroke.

Aeles, J.; Kelly, L. A.; Yoshitake, Y.; Cresswell, A. G.

doi: 10.1152/jn.00023.2020pmid: 32267195

We recorded for the first time single motor unit action potential trains in the flexor hallucis brevis, a short toe muscle, over the full range of maximum voluntary contraction. Its motor units are recruited up to very high (98%) recruitment thresholds with a substantial range of discharge rates. We further show high variability with crossover of discharge rates as a function of recruitment threshold both between participants and between motor units within participants.

Cirillo, John; Mooney, Ronan A.; Ackerley, Suzanne J.; Barber, P. Alan; Borges, Victor M.; Clarkson, Andrew N.; Mangold, Christine; Ren, April; Smith, Marie-Claire; Stinear, Cathy M.; Byblow, Winston D.

doi: 10.1152/jn.00561.2019pmid: 32186435

Magnetic resonance spectroscopy indicated higher excitation-inhibition ratios within motor cortex during subacute recovery than age-similar healthy controls. Measures obtained from adaptive threshold hunting paired-pulse transcranial magnetic stimulation indicated greater tonic inhibition in patients compared with controls. Therapeutic approaches that aim to normalize motor cortex inhibition during the subacute stage of recovery should be explored.

Dorkoski, Ryan; Hancock, Kenneth E.; Whaley, Gareth A.; Wohl, Timothy R.; Stroud, Noelle C.; Day, Mitchell L.

doi: 10.1152/jn.00713.2019pmid: 32186439

A “division of labor” has previously been assumed in which the directions of low- and high-frequency sound sources are thought to be encoded by neurons preferentially sensitive to low and high frequencies, respectively. Contrary to this, we found that auditory midbrain neurons encode the directions of both low- and high-frequency sounds regardless of their preferred frequencies. Neural responses were shaped by different sound localization cues depending on the stimulus spectrum—even within the same neuron.

Taube, Jeffrey S.; Shinder, Michael E.

doi: 10.1152/jn.00475.2019pmid: 32208877

A major question in the field of spatial cognition is how animals represent three-dimensional (3D) space. Different results have been obtained across various species and may depend on whether the species inhabits a 3D environment or is terrestrial (land dwelling). The head direction (HD) cell system is an attractive candidate to study in terms of 3D representations. HD cells fire as a function of the animal’s directional heading in the horizontal plane, independent of the animal’s location and on-going behavior. Another issue concerns whether HD cells are tuned in 3D space or tuned to the 2D horizontal plane. Shinder and Taube (Shinder ME, Taube JS. J Neurophysiol 121: 4–37, 2019) addressed this issue by manipulating a rat’s orientation in 3D space while monitoring responses from classic HD cells in the rat anterodorsal thalamus. They reported that HD cells did not display conjunctive firing with pitch or roll orientations. Direction-specific firing was primarily derived from horizontal semicircular canal information and that the gravity vector played an important role in influencing the cell’s firing rate and its preferred firing direction. Laurens and Angelaki (Laurens J, Angelaki DE. J Neurophysiol 122: 1274–1287, 2019) challenged this view by performing a mathematical analysis on the Shinder and Taube data and concluded that they would not have seen 3D tuning based on their experimental approach. We provide a historical review of these issues followed by a summary of the experiments, which includes additional analyses. We then define what it means for a HD cell to be tuned in 3D and finish by rebutting the reanalyses performed by Laurens and Angelaki.

Bligard, Gregory W.; DeBrecht, James; Smith, Robert G.; Lukasiewicz, Peter D.

doi: 10.1152/jn.00527.2019pmid: 32233906

Excitatory amino acid transporter 5 (EAAT5) glutamate transporters have a chloride channel that is strongly activated by glutamate, which modulates excitatory signaling. We found that EAAT5 is a major contributor to feedback inhibition on rod bipolar cells. Inhibition to rod bipolar cells is also mediated by GABA and glycine. GABA and glycine mediate the early phase of feedback inhibition, and EAAT5 mediates a more delayed inhibition. Together, inhibitory transmitters and EAAT5 coordinate to mediate feedback inhibition, controlling neuronal output.