In this Issue
REVIEW | Biology of Neuroengineering Interfaces
REVIEW | Comparative Approaches in Neurobiology
RESEARCH ARTICLE | Active Sensing
- Variations in vibrissal geometry across the rat mystacial pad: base diameter, medulla, and taper
Rats tactually explore their world by brushing and tapping their whiskers against objects. Each whisker's geometry will have a large influence on its mechanics and thus on the tactile signals the rat obtains. We performed a meta-analysis of seven studies to generate equations that describe systematic variations in whisker geometry across the rat's face. We also quantified the geometry of the whisker medulla. A database provides access to geometric parameters of over 500 rat whiskers.
RESEARCH ARTICLES | Cellular and Molecular Properties of Neurons
- Furosemide depresses the presynaptic fiber volley and modifies frequency-dependent axonal excitability in rat hippocampus
This study shows that the anion transporter antagonists furosemide and DIDS cause a marked decrease of axonal excitability in rat hippocampal CA1 region and prevent the induction of activity-dependent hyperexcitability in Schaffer collateral axons. The data are consistent with direct effects on axonal membrane properties. We also find that activity-dependent enhancement and depression of axonal excitability can be modified independently, suggesting that these events are governed by different underlying processes.
- Developmental nicotine exposure alters potassium currents in hypoglossal motoneurons of neonatal rat
Developmental nicotine exposure is associated with increased cell excitability, which is often accompanied by compensatory changes aimed at normalizing excitability. Here we show that whole cell potassium currents are also increased in hypoglossal motoneurons from nicotine-exposed neonatal rats under conditions of increased cell and network excitability. This is consistent with a compensatory response aimed at preventing instability under conditions in which excitatory synaptic input is high and is compatible with the concept of homeostatic plasticity.
- Nonlinear effects of hyperpolarizing shifts in activation of mutant Nav1.7 channels on resting membrane potential
Inherited erythromelalgia (IEM), the first human pain disorder linked to a sodium channel, is widely regarded as a genetic model of neuropathic pain. IEM is produced by Nav1.7 mutations that hyperpolarize activation. These mutations produce a depolarization of resting membrane potential (RMP) in dorsal root ganglion neurons. Using dynamic clamp to explore the effect on RMP of the shift in activation, we demonstrate a nonlinear effect on RMP as the shift in activation voltage dependence becomes more hyperpolarized.
RESEARCH ARTICLES | Control of Movement
- Motor plan differs for young and older adults during similar movements
We aimed to determine whether the altered activation of muscles in older adults compared with young adults during fast goal-directed movements is related to an altered motor plan. For matched movements, there were differences in the coordination of antagonistic muscles but no differences in the individual activation of muscles. We provide novel evidence that the differential activation of muscles in older adults is related to an altered motor plan.
- Muscle spindles in human tibialis anterior encode muscle fascicle length changes
Muscle spindles are exquisitely sensitive to changes in muscle length, but recordings from human muscle spindle afferents are usually correlated with joint angle rather than muscle fascicle length. In this study, we monitored both muscle fascicle length and spindle firing from the human tibialis anterior muscle in vivo. Our findings are the first to measure these signals in vivo and provide an experimental basis for exploring this link further.
- Distribution of TTX-sensitive voltage-gated sodium channels in primary sensory endings of mammalian muscle spindles
The molecular mechanisms underlying mechanosensory signaling responsible for proprioceptive functions are not completely elucidated. This study provides the first evidence that voltage-gated sodium channels (NaVs) are expressed in the spindle primary sensory ending, where they are found at every site involved in transduction or encoding of muscle stretch. We propose that NaVs contribute to multiple steps in sensory signaling by muscle spindles, as it does in other types of slowly adapting sensory neurons.
- Fractionation of muscle activity in rapid responses to startling cues
We demonstrate that the ability to activate muscles selectively is preserved during the very rapid reactions produced following a startling cue. This suggests that the contributions from different descending pathways are comparable between these rapid reactions and more typical voluntary movements.
RESEARCH ARTICLE | Glial Cells and Neuronal Signaling
- Minocycline blocks glial cell activation and ventilatory acclimatization to hypoxia
The signals for neural plasticity in medullary respiratory centers underlying ventilatory acclimatization to chronic hypoxia are unknown. We show that chronic hypoxia activates microglia and subsequently astrocytes. Minocycline, an antibiotic that blocks microglial activation and has anti-inflammatory properties, also blocks astrocyte activation in respiratory centers during chronic hypoxia and ventilatory acclimatization. However, minocycline cannot reverse ventilatory acclimatization after it is established. Hence, glial cells may provide signals that initiate but do not sustain ventilatory acclimatization.
RESEARCH ARTICLES | Higher Neural Functions and Behavior
- Role of the cerebellum in high stages of motor planning hierarchy
Traditionally, the cerebellum was considered essential for motor planning. By studying an extremely rare patient with cerebellar agenesis and a group of neurotypical controls, we found that high stages of the motor planning hierarchy can be preserved even in this patient with congenital absence of the cerebellum. Our results provide interesting insights that shed light on the neural circuits supporting distinct levels of motor planning. Furthermore, the results are intriguing because of their potential clinical implications in autism.
- In monkeys making value-based decisions, amygdala neurons are sensitive to cue value as distinct from cue salience
This is the first study to characterize amygdala neuronal responses to cues predicting rewards and penalties of variable size in monkeys making value-based choices. Manipulating reward and penalty size allowed distinguishing activity dependent on motivational salience from activity dependent on value. This approach revealed in a previous study that neurons of area lateral intraparietal (LIP) encode motivational salience. Here, it reveals that amygdala neurons encode value. The results establish a sharp functional distinction between the two areas.
- Perceptual attraction in tool use: evidence for a reliability-based weighting mechanism
Kinematic tool use is associated with a perceptual attraction between the spatially separated hand and the effective part of the tool. We provide a formal account for this phenomenon, thereby showing that the process behind it is similar to optimal integration of sensory information relating to single objects.
- Conjoint representation of texture ensemble and location in the parahippocampal place area
This study investigates how the parahippocampal place area (PPA) represents texture information within a scene context. We claim that texture is represented in the PPA at multiple levels: the texture ensemble information at the across-voxel level and the conjoint information of texture and its location at the within-voxel level. The study proposes a working hypothesis that reconciles contrasting results from multivoxel pattern analysis and repetition suppression, suggesting that the methods are complementary to each other but not necessarily interchangeable.
- A neural locus for spatial-frequency specific saccadic suppression in visual-motor neurons of the primate superior colliculus
Saccades, which repeatedly realign the line of sight, introduce spurious signals in retinal images that normally go unnoticed. In part, this happens because of perisaccadic suppression of visual sensitivity, which is known to depend on spatial frequency. We discovered that a specific subtype of superior colliculus (SC) neurons demonstrates spatial-frequency-dependent suppression. Curiously, it is the neurons that help mediate the saccadic command itself that exhibit such suppression, and not the purely visual ones.
- Modulation of motor cortex inhibition during motor imagery
This is the first study to investigate how 1-ms short-interval intracortical inhibition, long-interval intracortical inhibition, and late cortical disinhibition are modulated during motor imagery and voluntary muscle relaxation. We present novel findings of decreased 100-ms long-interval intracortical inhibition during voluntary muscle relaxation and increased late cortical disinhibition during both motor imagery and voluntary muscle relaxation.
RESEARCH ARTICLES | Nervous System Pathophysiology
- Characterizing differential poststroke corticomotor drive to the dorsi- and plantarflexor muscles during resting and volitional muscle activation
The present study observed that lower-limb corticomotor asymmetry resulted from both reduced paretic and enhanced nonparetic limb corticomotor excitability compared with neurologically intact controls. The most asymmetrical corticomotor drive was observed in the plantarflexor muscles of individuals with poor poststroke walking recovery. This suggests that neural function of dorsi- and plantarflexor muscles in both paretic and nonparetic limbs may play a role in poststroke walking function, which may have important implications when developing targeted poststroke rehabilitation programs to improve walking ability.
- Magnetic resonance spectroscopy of current hand amputees reveals evidence for neuronal-level changes in former sensorimotor cortex
This study is the first to use functional magnetic resonance-guided magnetic resonance spectroscopy to examine neurochemical mechanisms underlying functional reorganization in the primary somatosensory and motor cortices consequent to upper extremity amputation and its potential reversal through hand replantation or transplantation. We provide evidence for selective alteration of cortical neuronal integrity associated with amputation-related deafferentation that may not be reversible.
- High cardiorespiratory fitness in early to late middle age preserves the cortical circuitry associated with brain-heart integration during volitional exercise
Our first observation suggests that fitness does not strongly predict the heart rate (HR) response to a volitional handgrip task in middle- to older-aged adults. Second, the BOLD response associated with the handgrip task, and with the HR time course, was associated with response patterns in the cortical autonomic network. Finally, whereas high cardiorespiratory fitness failed to affect absolute HR responses to isometric handgrip in this age range, a select effect was observed in cortical regions known to be associated with cardiovascular arousal, beyond that achieved through healthy active living.
RESEARCH ARTICLES | Neural Circuits
- Dissociation between sustained single-neuron spiking and transient β-LFP oscillations in primate motor cortex
We show that whereas motor cortex spiking rates and beta (~20 Hz) spiking rhythmicity remain sustained during steady-state movement preparation periods, β-local field potential (β-LFP) oscillations emerge, in contrast, as transient events. Furthermore, the β-LFP phase at which neurons spike drifts: phase coupling is typically weak or absent. This dissociation points to two sources of variation in the level of motor cortex beta: one that impacts single-neuron spiking and another related to the generation of measured mesoscopic β-LFPs.
- Spontaneous dynamics of neural networks in deep layers of prefrontal cortex
Using calcium imaging and a novel analytic framework, we characterized the spontaneous and NMDA-evoked activity of layer 5 prefrontal cortex at a largely unexplored spatiotemporal scale. Our results suggest that the mPFC microcircuitry is capable of intrinsically generating delta oscillations and sustaining synchronized network activity that is potentially relevant for understanding its contribution to cognitive processes.
- Frequency tuning of synaptic inhibition underlying duration-tuned neurons in the mammalian inferior colliculus
Duration-tuned neurons (DTNs) arise from temporally offset excitatory and inhibitory synaptic inputs. We used single-unit recording and paired-tone stimulation to measure the spectral tuning of the inhibitory inputs to DTNs. The onset of inhibition was independent of stimulus frequency; the offset and duration of inhibition systematically decreased as the stimulus departed from the cell’s best excitatory frequency. Best inhibitory frequencies matched best excitatory frequencies; however, inhibitory bandwidths were more broadly tuned than excitatory bandwidths.
- A circuit for saccadic suppression in the primate brain
A fundamental puzzle in visual neuroscience is that we frequently make rapid eye movements (saccades) but seldom perceive the visual blur accompanying each movement. We investigated neuronal correlates of this saccadic suppression by recording from and perturbing a recently identified circuit from brainstem to cortex. We found suppression at each stage, with evidence that it was driven by an internally generated signal. We conclude that this circuit contributes to neuronal suppression of visual signals during eye movements.
- Correlation between discharge timings of pairs of motor units reveals the presence but not the proportion of common synaptic input to motor neurons
The strength of correlation between output spike trains is only poorly associated with the degree of common input to the population of motor neurons. The synchronization between motor unit firing trains is necessarily caused by the (functional) common input to motor neurons, but it is not possible to infer the degree of shared common input to a pair of motor neurons on the basis of correlation measures of their output spike trains.
RESEARCH ARTICLES | Sensory Processing
- The mammalian efferent vestibular system plays a crucial role in vestibulo-ocular reflex compensation after unilateral labyrinthectomy
Loss of the α9-nicotinic acetylcholine receptor (α9-nAChR) subunit utilized by the efferent vestibular system (EVS) has been shown to significantly affect vestibulo-ocular reflex (VOR) adaptation. In our present study we have shown that loss of α9-nAChRs also affects VOR compensation, suggesting that the mammalian EVS plays an important role in vestibular plasticity, in general, and that VOR compensation is a more distributed process than previously thought, relying on both central and peripheral changes.
- Maps of cone opsin input to mouse V1 and higher visual areas
Two elements of this study are particularly novel. For one, it is the first to quantify cone inputs to mouse visual cortex; we have measured cone input in five visual areas. Next, it is the first study to identify a feature map in the mouse visual cortex that is based on well-characterized anisotropy of cones in the retina; we have identified maps of opsin selectivity in five visual areas.
- Characteristics of the local cutaneous sensory thermoneutral zone
Contrary to a widespread concept in human thermoreception, we show that local sensory thermoneutrality is achievable outside the 32–34°C skin temperature range. We propose that sensory adaption underlies a new mechanism of temperature integration. Also, we have developed from vision research a new quantitative test addressing the balance in activity of cutaneous cold and warm thermoreceptors. This could have important clinical (assessment of somatosensory abnormalities in neurological disease) and applied (design of personal comfort systems) implications.
- Spatial cognition in a virtual reality home-cage extension for freely moving rodents
Virtual reality (VR) environments are a powerful tool for the investigation of brain mechanisms. We introduce the Servoball, a VR treadmill for freely moving rodents. The Servoball is integrated with the animals’ group home cage. Single individuals voluntarily enter using automated access control. Training is highly time efficient, even for cognitively complex VR paradigms.
RAPID REPORT | Control of Movement
- Microcircuit formation following transplantation of mouse embryonic stem cell-derived neurons in peripheral nerve
This manuscript demonstrates that, following peripheral transplantation of neurons derived from embryonic stem cells, the grafts are spontaneously active. The activity is produced and modulated by a number of transmitter systems, indicating that there is a degree of self-assembly of circuits in the grafts.
RAPID REPORT | Sensory Processing
- Optimal delineation of single C-tactile and C-nociceptive afferents in humans by latency slowing
Human skin encodes a plethora of touch interactions, and affective tactile information is primarily signaled by slowly conducting C-mechanoreceptive afferents. We show that electrical stimulation of low-threshold C-tactile afferents produces markedly different patterns of activity compared with high-threshold C-mechanoreceptive nociceptors, although the populations overlap in their responses to mechanical stimulation. This fundamental distinction demonstrates a divergence in affective touch signaling from the first stage of sensory processing, having implications for the processing of interpersonal touch.