In this Issue
REVIEW | Comparative Approaches in Neurobiology
RESEARCH ARTICLE | Active Sensing
- Keeping still doesn't “make sense”: examining a role for movement variability by stabilizing the arm during a postural control task
The role of movement variability during a static limb position task is currently unknown. We tested whether variability remains in the absence of sensory-based error with an apparatus that stabilized the limb without the participant's knowledge during a static postural task. Increased forces observed during arm stabilization predicted movements greater than those observed when not externally stabilized. These results suggest movement variability during static postures could facilitate the gathering of sensory information from the surrounding environment.
RESEARCH ARTICLES | Auditory System Plasticity
- Activity-dependent formation and location of voltage-gated sodium channel clusters at a CNS nerve terminal during postnatal development
Clustering of voltage-gated sodium (Nav) channels and their distribution along the axon, specifically at the unmyelinated axon segment next to the nerve terminal, are essential for tuning propagated action potentials. Nav channel clusters near the nerve terminal and their location as a function of neuronal position along the mediolateral axis are controlled by auditory inputs after hearing onset. Thus sound-mediated neuronal activity influences the tonotopic organization of Nav channels at the nerve terminal in the auditory brain stem.
- Context-dependent plasticity in the subcortical encoding of linguistic pitch patterns
Human auditory perception in dynamic listening environments requires fine-tuning of sensory signal based on behaviorally relevant regularities in listening context, i.e., online experience-dependent plasticity. Our finding suggests what partly underlie online experience-dependent plasticity are interplaying contextual processes in the subcortical auditory system that are responsive to predictability as well as novelty in listening context. These findings add to the literature that looks to establish the neurophysiological bases of auditory system plasticity, a central issue in auditory neuroscience.
- Maintenance of neuronal size gradient in MNTB requires sound-evoked activity
Neurons of the medial nucleus of the trapezoid body (MNTB) act as fast-spiking inhibitory interneurons within the auditory brain stem. The MNTB is topographically organized, with low sound frequencies encoded laterally and high frequencies medially. We discovered a cell size gradient along this axis: lateral neurons are larger than medial neurons. The absence of this gradient in deaf mice lacking plasma membrane calcium ATPase 2 suggests an activity-dependent, calcium-mediated mechanism that controls neuronal soma size.
RESEARCH ARTICLES | Cellular and Molecular Properties of Neurons
- Cocaine sensitization increases subthreshold activity in dopamine neurons from the ventral tegmental area
This work uses a new approach that directly extracts important biophysical parameters from alpha function-evoked synaptic potentials. Two of these parameters are the cell membrane capacitance (Cm) and rate at any time point of the synaptic waveform. The use of such methodology shows that cocaine sensitization reduces Cm and increases the speed of synaptic signaling. Paradoxically, although synaptic potentials show a faster decay under cocaine their temporal summation is substantially elevated.
- The role of retinoic acid in the formation and modulation of invertebrate central synapses
This study performed the first electrophysiological analysis of the ability of the vitamin A metabolite, retinoic acid, to exert trophic influences during synaptogenesis independently of its effects in supporting neurite outgrowth. It was also the first study to examine the ability of retinoic acid to modify both chemical and electrical synapses in any invertebrate, nonchordate species. We provide evidence that all-trans retinoic acid can modify invertebrate electrical synapses of central neurons in a cell-specific manner.
RESEARCH ARTICLE | Comparative Approaches in Neurobiology
- Cortical plasticity following stripe rearing in the marsupial Monodelphis domestica: neural response properties of V1
These results are the first description of visual response properties of the most commonly studied marsupial model organism, the short-tailed opossum (Monodelphis domestica). Further, these results are the first to demonstrate experience-dependent plasticity in the visual system of a marsupial species. Thus the ability of cortical neurons to alter their properties based on the dynamics of the visual environment predates the emergence of eutherian mammals and was likely present in our earliest mammalian ancestors.
RESEARCH ARTICLE | Control of Homeostasis
- Role of fructose and fructokinase in acute dehydration-induced vasopressin gene expression and secretion in mice
This study increases our understanding of the mechanisms leading to vasopressin release under conditions of water restriction (acute dehydration). Specifically, these studies suggest that the aldose reductase-fructokinase pathways may be involved in vasopressin synthesis in the hypothalamus and secretion by the pituitary in response to acute dehydration. Nevertheless, mice undergoing water restriction remain capable of maintaining sufficient vasopressin (copeptin) levels to allow normal urinary concentration. Further studies of the aldose reductase-fructokinase system in vasopressin regulation appear indicated.
RESEARCH ARTICLES | Control of Movement
- Foot placement relies on state estimation during visually guided walking
Accurate foot placement is essential for safe walking. We used computational models and human walking experiments to test how our nervous system achieves this accuracy. We find that our control of foot placement beneficially combines sensory feedback with internal forward model predictions to accurately estimate the body's state. Our results match recent computational neuroscience findings for reaching movements, suggesting that state estimation is a general mechanism of human motor control.
- Neuromuscular responses differ between slip-induced falls and recoveries in older adults
A central question relevant to the prevention of falls is: How does the robust control of walking and balance break down during a fall? Previous work has focused on muscle coordination during successful balance recoveries or the kinematics and kinetics of falls. Here, for the first time, we identified differences in the spatial and temporal coordination of muscles among older adults who fell and those who recovered from an unexpected slip.
- Parietal area BA7 integrates motor programs for reaching, grasping, and bimanual coordination
Our manuscript describes a role of human Brodmann area 7 (BA7) in the integration of multiple visuomotor programs for reaching, grasping, and bimanual coordination. Our results are the first to suggest that right BA7 is critically involved in the coordination of reach-to-grasp movements of the two arms. The results complement previous reports of right-hemisphere lateralization for bimanual grasps.
- Contributions of rapid neuromuscular transmission to the fine control of acoustic parameters of birdsong
It is largely unknown how fine motor control of acoustic parameters is achieved in vocal organs. Subtle manipulation of syringeal muscle function was used to test how active motor control influences acoustic parameters. Slowed activation kinetics of muscles reduced frequency modulation and, unexpectedly, caused a distinct decrease in sound amplitude and increase in phonation onset pressure. These results show that active control enhances the efficiency of energy conversion in the syrinx.
- Neural coupling between homologous muscles during bimanual tasks: effects of visual and somatosensory feedback
This study investigated the effects of somatosensory feedback during bimanual tasks on the neural coupling between arm muscles, which remains largely unexplored. Somatosensory feedback using a balancing apparatus, compared with visual feedback, significantly increased neural coupling between homologous muscles (indicated by intermuscular coherence values) and improved temporal correlation of bilateral force production. Notably, feedback type modulated coherence in the α- and γ-bands (more subcortical pathways), whereas task type mainly affected β-band coherence (corticospinal pathway).
- Using noise to shape motor learning
Many theories argue that we choose to make the specific movements that minimize motor noise. Here, by changing the relationship between movements and noise, we show that people actively learn to make movements that minimize noise. This not only provides direct evidence for the theories of noise minimization but presents a way to use noise to teach specific movements to improve rehabilitative therapies and human-machine interface control.
- Muscle afferent excitability testing in spinal root-intact rats: dissociating peripheral afferent and efferent volleys generated by intraspinal microstimulation
Excitability testing of primary afferents has been used to evaluate presynaptic modulation of synaptic transmission in experiments conducted in vivo. However, to apply this method to muscle afferents of animals with intact spinal roots, it is crucial to dissociate antidromic and orthodromic volleys induced by spinal microstimulation. We propose a new method to make this dissociation possible without cutting spinal roots and demonstrate that it facilitates excitability testing of muscle afferents.
RESEARCH ARTICLES | Higher Neural Functions and Behavior
- Trial-to-trial adjustments of speed-accuracy trade-offs in premotor and primary motor cortex
Setting the speed-accuracy trade-off (SAT) is crucial for efficient decision making. Previous studies have reported that subjects adjust their SAT after individual decisions, usually choosing more conservatively after errors, but the neural correlates of this phenomenon are only partially known. Here, we show that neurons in PMd and M1 of monkeys performing a reach decision task support this mechanism by adequately modulating their firing rate as a function of the outcome of the previous decision.
- Neuronal pattern separation of motion-relevant input in LIP activity
A new hypothesis is proposed on the role of the lateral intraparietal (LIP) region of cortex during rapid decision making. This hypothesis suggests that LIP alters the representation of ambiguous inputs to reduce their overlap, thus improving sensory discrimination. A combination of computational modeling, theoretical analysis, and electrophysiological data shows that the pattern separation hypothesis links neural activity to behavior and offers novel predictions on the role of LIP during sensory discrimination.
- Spatial scale and distribution of neurovascular signals underlying decoding of orientation and eye of origin from fMRI data
Large-scale response biases can account for decoding of orientation and eye of origin in human early visual areas V1–V3. For eye of origin this pattern is a nasotemporal bias; for orientation it is a radial bias. Differences in decoding performance across areas and stimulus features are not well predicted by differences in columnar-scale organization of each feature. Large-scale biases in extrastriate areas are spatially correlated with those in V1, suggesting biases originate in primary visual cortex.
RESEARCH ARTICLES | Nervous System Pathophysiology
- BDNF effects on functional recovery across motor behaviors after cervical spinal cord injury
This study demonstrates that after unilateral C2 spinal cord hemisection (SH), there are differences in the spontaneous recovery of diaphragm (DIAm) electromyographic activity during ventilatory compared with more forceful, nonventilatory motor behaviors. Furthermore, we show that intrathecal delivery of brain-derived neurotrophic factor (BDNF) at the level of the phrenic motor neuron pool enhances recovery of ipsilateral DIAm activity following SH, exerting main effects on recovery of ventilatory but not higher force, nonventilatory behaviors.
- Diaphragm electromyographic activity following unilateral midcervical contusion injury in rats
The present study shows that unilateral contusion injury at C4 results in substantial loss of phrenic motoneurons but increased diaphragm muscle activity across a range of ventilatory and higher force, nonventilatory behaviors. Measures of neural drive indicate increased descending input to phrenic motoneurons that was more pronounced during higher force, nonventilatory behaviors. These findings reveal novel, complex adaptations in neuromotor control following injury, suggestive of increased recruitment of more fatigable, high-threshold motor units.
- Increases in human motoneuron excitability after cervical spinal cord injury depend on the level of injury
Unitary F waves were common in paralyzed thenar muscles of people who had a chronic spinal cord injury (SCI) at the C4 level compared with uninjured people, but F waves did not occur in people that had SCI at the C5 or C6 level. These results highlight that intrinsic motoneuron excitability depends, in part, on how close the motoneurons are to the site of the spinal injury, which could alter the generation and strength of voluntary and involuntary muscle contractions.
RESEARCH ARTICLE | Neural Circuits
- Intra- and interregional cortical interactions related to sharp-wave ripples and dentate spikes
Off-line cortico-hippocampal interactions are thought to support memory consolidation. We surveyed the relationship between hippocampal sharp-wave ripples (SWRs) and dentate spikes (DSs) with up-states across multiple cortical regions. SWRs and DSs were associated with increased cortical gamma oscillations. Interregional gamma coherence rose much more strongly in relation to DSs than to SWRs. Moreover, it was time locked to DSs but not SWRs. These results have important implications for current theories of systems memory consolidation during sleep.
RESEARCH ARTICLES | Sensory Processing
- Contrast sensitivity, V1 neural activity, and natural vision
Visual sensitivity and activity in brain area V1 were studied in a paradigm that included saccadic eye movements and natural visual input. V1 responses and contrast sensitivity were significantly reduced compared with results in common laboratory paradigms. The parallel neural and perceptual effects of eye movements and stimulus complexity appear to be due to a form of rapid adaptation that carries across saccades.
- Functional role of airflow-sensing hairs on the bat wing
Bat wings are adaptive airfoils that enable demanding flight maneuvers. The bat wing is sparsely covered with sensory hairs, and wing-hair removal results in reduced flight maneuverability. Here, we report for the first time single-neuron responses recorded from primary somatosensory cortex to airflow stimulation that varied in amplitude, duration, and direction. The neurons show high sensitivity to the directionality of airflow and might act as stall detectors.
- Contextual effects of noise on vocalization encoding in primary auditory cortex
The understanding of where and how auditory scene analysis is accomplished is of broad interest to neuroscientists. In this paper, we systematically investigated neuronal coding of multiple vocalizations degraded by two distinct noises at various signal-to-noise ratios in nonhuman primates. In the process, we uncovered heterogeneity of single-unit representations for different auditory scenes yet homogeneity of responses across the population.
- Body sway adaptation to addition but not withdrawal of stabilizing visual information is delayed by a concurrent cognitive task
This study is the first to test the effect of an arithmetic task on the time course of balance readjustment following visual withdrawal or addition. Performing such a cognitive task increases the time delay following addition of vision but has no effect on withdrawal dynamics. This suggests that sensorimotor integration following addition of a stabilizing signal is performed at a cortical level, whereas the response to its withdrawal is “automatic” and accomplished at a subcortical level.
- Automated classification of pain perception using high-density electroencephalography data
The development of a biological marker for pain continues to gain traction in literature. Our findings show that high- and low-pain perception in human subjects can be classified with 89% accuracy using high-density EEG data from prefrontal cortex and contralateral sensorimotor cortex. Our approach represents a novel neurophysiological paradigm that advances the literature on biological markers for pain.
- Spatiotopic coding during dynamic head tilt
Given that spatiotopic coding could play a key role in maintaining visual stability, we look for evidence of spatiotopic coding after retinal image transformations caused by head tilt. To this end, we measure the strength of the positional motion aftereffect (PMAE; previously shown to be largely spatiotopic after saccades) after large head tilts. We find that, as with eye movements, the spatial selectivity of the PMAE has a large spatiotopic component after head rotation.
- Comodulation masking release in the inferior colliculus by combined signal enhancement and masker reduction
The detection of comodulation, i.e., coherent level fluctuations in different frequency regions, is an important feature of speech recognition. In this study, we demonstrate how the representation of a signal in comodulated masking conditions changes along the auditory pathway by using a stimulus paradigm from the cochlea nucleus for the first time in the inferior colliculus. This happens on a timescale that makes corticocollicular feedback a likely candidate as the source.
RESEARCH ARTICLES | Spinal Control of Motor Outputs
- Intraspinal microstimulation and diaphragm activation after cervical spinal cord injury
We examined the feasibility of using intraspinal microstimulation (ISMS) of the cervical spinal cord to evoke diaphragm activity ipsilateral to acute and subacute hemisection of the upper cervical spinal cord of the rat. This proof-of-concept study demonstrated the efficacy of diaphragm activation, using an upper airway respiratory EMG signal to trigger ISMS at the level of the ipsilesional phrenic nucleus during acute and advanced postinjury intervals.
- Adenosine-dependent phrenic motor facilitation is inflammation resistant
This study gives novel insights concerning how a mild systemic inflammation impacts phrenic motor plasticity (pMF), particularly adenosine-dependent pMF. We suggest that since this adenosine-dependent pathway is insensitive to systemic inflammation, it represents an alternative or “backup” mechanism of pMF when other mechanisms are suppressed.
- Postural threat influences vestibular-evoked muscular responses
This is the first study to show increases in vestibular-evoked responses of the lower body muscles under conditions of increased threat of postural perturbation. While robust findings were observed in hip and leg muscles, less consistent results were found in muscles of the trunk. The present findings provide further support in the ongoing debate for arguments that vestibular-evoked balance responses are influenced by fear and anxiety and explain previous threat-related changes in balance.