Journal of Neurophysiology

van Helden, Joeri F. L.; Cabral, Hélio V.; Alexander, Emma; Strutton, Paul H.; Martinez-Valdes, Eduardo; Falla, Deborah; Chowdhury, Joy Roy; Chiou, Shin-Yi

doi: 10.1152/jn.00246.2024pmid: 39828930

Many individuals with incomplete spinal cord injury (SCI) exhibit reduced volitional control of trunk muscles, such as impaired voluntary contractions of the erector spinae (ES), due to damage to the neural pathways regulating sensorimotor function. Studies using conventional bipolar electromyography (EMG) showed alterations in the overall, or global, activation of the trunk muscles in people with SCI. However, how activation varied across specific regions within the ES, referred to as regional activation, remains unknown. The aim of the study was to investigate the regional distribution of the ES activity below the level of injury in individuals with incomplete SCI during postural tasks and multidirectional reaching tasks using high-density EMG. Twenty-one individuals with incomplete SCI and age-matched controls were recruited. The EMG amplitude of the thoracic ES and displacement of the arm, trunk, and center of pressure were recorded during the tasks. Activation was more in the lower region of the ES in individuals with SCI compared with the controls during the postural tasks. Additionally, activation was limited to a small area of the ES during the reaching tasks. The EMG amplitude was greater during reaching forward than returning to the upright posture in the controls; however, this phase-dependent difference in the EMG amplitude was not present in individuals with SCI. Our findings demonstrate changes in regional activation of the thoracic ES during postural and reaching tasks, likely reflecting injury-induced changes in selective neural control to activate residual muscle fibers of the ES for postural control and function after SCI.

Khan, Zainab; Messiri, Nour El; Iqbal, Emann; Hassan, Hadi; Tanweer, Mohammad S.; Sadia, Syeda R.; Taj, Moizzuddin; Zaidi, Umar; Yusuf, Kamran; Syed, Naweed I.; Zaidi, Mukarram

doi: 10.1152/jn.00345.2024pmid: 39842807

Stress is a fundamental adaptive response mediated by the amygdala and Hypothalamus-Pituitary-Adrenal (HPA) axis. Extreme or chronic stress, however, can result in a multitude of neuropsychiatric disorders, including anxiety, paranoia, bipolar disorder (BP), major depressive disorder (MDD), and Post-Traumatic Stress Disorder (PTSD). Despite widespread exposure to trauma (70.4%), the incidence of PTSD is relatively low (6.8%), suggesting that either individual susceptibility or adaptability driven by epigenetic and genetic mechanisms are likely at play. PTSD takes hold from exposure to traumatic events, such as death threats or severe abuse, with its severity being impacted by the magnitude of trauma, it's frequency, and the nature. This comprehensive review examines how traumatic experiences and epigenetic modifications in hypothalamic pituitary axis (HPA), such as DNA methylation, histone modifications, non-coding RNAs, and chromatin remodeling, are transmitted across generations, and impact genes like FKBP5, NR3C1, BDNF, and SLC6A4. It also provides a comprehensive overview on trauma reversal, resilience mechanisms, and pro-resilience factors such as HATs/HDACs ratio, DHEA/Cortisol ratio, testosterone levels, and neuropeptide Y, thus highlighting potential therapeutic approaches for trauma-related disorders. The studies highlighted here underscore the narrative, for the first time, that the examination and treatment of PTSD and other depressive disorders must invoke a multitude of approaches to seek out the most effective and personalized strategies. We also hope that the discussion emanating from this review will also inform government policies directed towards intergenerational trauma and PTSD.

Berg, D.; Hamernik, W.; Anderson, A.; Rochelle, L.; Blake, B.

doi: 10.1152/jn.00514.2024pmid: 39869022

Ballet shows numerous physiological benefits for dancers, with adaptations in posture, power, strength, stamina, and balance. The recent study from Simpkins and Yang (2024) showed 45% of ballet-trained dancers experienced a fall during a standing-slip perturbation, compared with 82.6% of non-dancers; along with shorter step latencies, durations, and speeds, which were accompanied by shorter electromyographic latencies in several leg muscles. This study demonstrates the viability of ballet training in aiding fall prevention in elderly individuals.

Nehrujee, Aravind; Rymer, W. Zev; Sandhu, Milap S.

doi: 10.1152/jn.00026.2025pmid: 39903171

Hua, An-Ke; Bai, Jing-Yuan; Wang, Guo-Zheng; Hao, Zeng-Ming; Meng, Jun; Wang, Jian

doi: 10.1152/jn.00350.2024pmid: 39866137

Human postural control system has the capacity to adapt to balance-challenging perturbations. However, the characteristics and mechanisms of postural adaptation to continuous perturbation under the sensory conflicting environments remain unclear. We aimed to investigate the functional role of oscillatory coupling drive to lower-limb muscles with changes in balance control during postural adaptation under multisensory congruent and incongruent environments. We combined a platform moving sinusoidally (0.24Hz) along the anterior-posterior (AP) axis and a virtual scene moving sinusoidally (0.24Hz) either along the AP or the medio-lateral (ML) axis to present a 3-min visual-somatosensory congruent condition (n=10) or incongruent condition(n=12), respectively. We analyzed the kinematic data, and performed intermuscular coherence analysis of surface EMG data from bilateral lower limbs. We found that the inter-limb coherence was larger under the congruent condition and decreased over the 3-min perturbation, while inter-limb coherence remained low and showed no changes under the incongruent condition over the 3-min perturbation. These results suggest that exposure to the incongruent condition disrupted inter-limb intermuscular coupling. Besides, we found the bilateral intra-limb coherence decreased over 3-min congruent and incongruent perturbation, with the bilateral ankle joint angular velocity decreased and the coupling strength (0.2-0.3Hz) between whole-body sway and sinusoidal stimuli in AP decreased. These findings suggest that continuous exposure to sinusoidal perturbation in AP under congruent and incongruent conditions decreased bilateral intermuscular coupling, contributing to flexibility in the sagittal plane. Overall, we suggested the postural control system adapts context-specifically to different sensory environments, with distinct characteristics of neuromuscular control strategies.

Zero, Alexander M.; Rice, Charles L.

doi: 10.1152/jn.00450.2024pmid: 39823194

The purpose was to assess whether visual feedback of torque contributes to motor unit (MU) firing rate reduction observed during post-activation potentiation (PAP) of skeletal muscle. From 15 participants 23 MUs were recorded with intramuscular fine-wire electrodes from the tibialis anterior during isometric dorsiflexion contractions at 20% of maximum, with and without both PAP and visual feedback of torque. A 5s maximal voluntary contraction (MVC) was used to induce PAP, and evoked twitch responses were assessed before and after. After the MVC twitch torque was 188% of baseline (p<0.001). Without visual feedback of torque and with participants targeting 20% MVC, torque, MU firing rates and rating of perceived exertion (RPE) were 22.8 ± 5.3 %MVC, 14.3 ± 2.6 Hz, 1.79 ± 0.93 a.u., respectively. Inducing PAP without feedback but targeting 20% MVC torque was overestimated by 50% (p<0.001) despite similar firing rates and RPE as baseline (both p≥0.3). With visual feedback, torque was not overestimated during PAP (p=0.14), however, rates and RPE were lower (13 and 20%, respectively) than baseline (both p≤0.008). Therefore, no compensatory modifications in MU output occurred despite muscle potentiation. This indicates lower voluntary drive, reflected additionally by reduced RPE, was responsible for the reduced firing rates so that torque did not exceed the required task, compared to modified peripheral feedback. During PAP, the motoneuron is not sensitive to alterations in the active state of the muscle unit per se, but rather compensatory adjustments to optimize contractile output are due to reductions in descending input.

Chen, Zhuo; Wang, Lin; Ying, Shaofei; Yuan, Jiaqi; Ren, Jiaxin; Yan, Ye; Qin, Yun; Liu, Tiejun; Yao, Dezhong

doi: 10.1152/jn.00484.2024pmid: 39842781

Based on item-method directed forgetting (DF) task, sixty participants were recruited to explore the influence of emotion (negative, neutral, and positive) on memory encoding processing. Behavioral results showed that participants were more successful at remembering negative pictures that needed to be forgotten, with both higher recognition rates and Pr values compared to neutral pictures. In the brain, parietal activities reflected preferential processing during negative picture viewing through enhanced late parietal positive potentials (LPP) relative to neutral ones. In addition, ‘Remember’ (R) instruction evoked a larger parietal P3 component, whereas ‘Forget’ (F) instruction evoked a stronger frontal N2 component, each of which component was significantly associated with the DF effect (i.e., more recognized items of R-cue than that of F-cue), reflecting the fact that inhibitory control and selective rehearsal mechanisms were jointly responsible for the directed forgetting of emotional materials. Finally, we showed the presence of instruction-evoked low-frequency phase synchronization between frontal and parietal regions, and that these synchronization patterns differed between R-cue and F-cue in an emotion-dependent manner. Together, these findings reveal cognitive mechanisms and specific patterns of large-scale phase synchronization underlying active forgetting of emotional memories, deepening our comprehension into the interplay between cognition and emotion.

Korkian, Yavar; Nakhla, Nardin; Pack, Christopher C.

doi: 10.1152/jn.00278.2024pmid: 39813398

Anatomical studies have revealed a prominent role for feedback projections in the primate visual cortex. Theoretical models suggest that these projections support important brain functions, like attention, prediction, and learning. However, these models make different predictions about the relationship between feedback connectivity and neuronal stimulus selectivity. We have therefore performed simultaneous recordings in different regions of the primate dorsal visual pathway. Specifically, we recorded neural activity from the medial superior temporal (MST) area, and one of its main feedback targets, the middle temporal (MT) area. We estimated functional connectivity from correlations in the single-neuron spike trains and performed electrical microstimulation in MST to determine its causal influence on MT. Both methods revealed that inhibitory feedback occurred more commonly when the source and target neurons had very different stimulus preferences. At the same time, the strength of feedback suppression was greater for neurons with similar preferences. Excitatory feedback projections, in contrast, showed no consistent relationship with stimulus preferences. These results suggest that corticocortical feedback could play a role in shaping sensory responses according to behavioral or environmental context.

Jung, Young Jun; Meffin, Hamish; Ibbotson, Michael R.

doi: 10.1152/jn.00352.2024pmid: 39887254

Orientation selectivity is a prominent feature of neurons in the mammalian primary visual cortex (V1), yet its emergence along the visual pathway varies across species. In carnivores and primates, neurons with elongated and orientation-selective receptive fields (RFs) emerge in V1, whereas in mice such RFs appear earlier, in the retina or dorsal lateral geniculate nucleus (dLGN). Here, we investigate the RF properties of neurons in the dLGN of a marsupial, the wallaby (Macropus eugenii) (N=2; Males), using multi-channel electrodes and nonlinear input model (NIM) analysis. Do dLGN RFs resemble those of carnivores and primates or exhibit unique characteristics, particularly regarding orientation selectivity? We found that 82% of neurons have a predominant ON-center response. We identified two main cell types: X-cells (N=15/22), which exhibit linear properties, and Y-cells (N=7/22), which display nonlinear characteristics. Most dLGN RFs were blob-like and lacked the oriented structures seen in cortical neurons but some had slightly elongated central areas. These results indicate that robust orientation selectivity develops fully in V1 (76% of neurons). However, mild orientation biases were observed in 41% of dLGN neurons. This study enhances our understanding of visual processing in marsupials and underscores the evolutionary significance of orientation selectivity in mammalian visual pathways.

Shanazz, Khadijah; Xie, Kun; Oliver, Tucker; Bogan, Jamal; Vale, Fernando L.; Sword, Jeremy; Kirov, Sergei A.; Terry, Alvin; O’Herron, Philip; Blake, David T.

doi: 10.1152/jn.00476.2024pmid: 39829107

Background: Deep brain stimulation (DBS) using electrical stimulation of neuronal tissue in the basal forebrain to enhance release of the neurotransmitter acetylcholine is under consideration to improve executive function in patients with dementia. While some small studies indicate a positive response in the clinical setting, the relationship between DBS and acetylcholine pharmacokinetics is incompletely understood. We examined the cortical acetylcholine response to different stimulation parameters of the basal forebrain. 2-photon in vivo imaging was combined with deep brain stimulation in C57BL/6J mice. Stimulating electrodes were implanted in the subpallidal basal forebrain, and the ipsilateral somatosensory cortex was imaged. Acetylcholine activity was determined using the GRABACh-3.0 acetylcholine receptor sensor, and blood vessels were visualized with Texas red. Experiments manipulating stimulation frequency demonstrated that integrated acetylcholine induced fluorescence was insensitive to frequency with the same number of pulses, and that maximum peak levels were achieved with frequencies from 60 to 130 Hz. Altering pulse train length indicated that longer stimulation resulted in higher peaks and more activation with sublinear summation. The acetylcholinesterase inhibitor, donepezil, increased the peak response to 10s of stimulation at 60Hz, and the integrated response increased 57% with the 2 mg/kg dose, and 126% with the 4 mg/kg dose. Acetylcholine levels returned to baseline with a time constant of 14 to 18 seconds. Donepezil increases total acetylcholine receptor activation associated with DBS but did not change temporal kinetics. The long time constants observed in the cerebral cortex add to the evidence supporting volume and synaptic neurotransmission.