Journal of Neurophysiology

Lane, John A.; Linden, David J.

doi: 10.1152/jn.00196.2009pmid: N/A

Shirvalkar, Prasad R.

doi: 10.1152/jn.91363.2008pmid: 19261704

Abstract The hippocampal formation is needed to encode episodic memories, which may be consciously recalled at some future time. This review examines recent advances in understanding recollection in the context of spatiotemporally organized relational memory coding and discusses predictions and challenges for future research on conscious remembering. Copyright © 2009 the American Physiological Society

Frigon, Alain

doi: 10.1152/jn.00003.2009pmid: 19279156

Abstract Within the spinal cord, the vast network of excitatory and inhibitory interneurons must be functionally reconfigured on an ongoing basis during locomotion to adapt to the environment and meet particular demands of the task. It is clear that different rhythmic motor behaviors are generated by shared and specialized circuitry and that reconfiguration is governed by multiple inputs that dynamically interact at the spinal level. Copyright © 2009 the American Physiological Society

Mandairon, Nathalie; Linster, Christiane

doi: 10.1152/jn.00076.2009pmid: 19261715

Abstract The adult mammalian olfactory bulb (OB) is unique in that olfactory sensory neurons project directly, without prior thalamic relay, to the OB. This review discusses evidence for the direct involvement of the OB in odor perception and its modulation by olfactory experience. We first discuss recent data showing that the OB exhibits a high level of plasticity in response to olfactory experience including exposure, enrichment, and learning. We next review evidence showing that, in return, experimental manipulation of the OB neural network changes how odorants are processed and perceived. We finally review in more detail a few experiments showing a tight correlation between the modulation of OB neural processing and odor perception. We argue that the OB has evolved to be an adapting network, allowing animals to adjust olfactory computations to changing environments. Copyright © 2009 the American Physiological Society

Kobayashi, K.; Winberry, J.; Liu, C. C.; Treede, R. D.; Lenz, F. A.

doi: 10.1152/jn.91347.2008pmid: 19244350

Abstract Cutaneous application of painful radiant heat laser pulses evokes potentials (laser-evoked potentials) that can be recorded from scalp or intracranial electrodes. We have now tested the hypothesis that the response of thalamic neurons to a cutaneous laser stimulus occurs at latencies predicted by the conduction delay between the periphery and the thalamus. We have carried out recordings from human thalamic neurons in the principal sensory nucleus (ventral caudal) in patients undergoing awake surgery for the treatment of tremor. The results demonstrate that many neurons respond to the laser with early and/or late latency peaks of activity, consistent with conduction of the response to the laser stimulus through pathways from Aδ and C fibers to the thalamus. These peaks were of short duration, perhaps due to the somatotopic- and modality-specific arrangements of afferent pathways to the thalamus. The responses of these thalamic neurons to the laser stimulus sometimes included low-threshold spike (LTS) bursts of action potentials, consistent with previous studies of different painful stimuli. A prior study has demonstrated that spike trains characterized by common LTS bursts such as the intermediate (I) category spontaneously change their category more commonly than do those without LTS bursts (NG: nongrouped category) during changes in the cognitive task. Spike trains of laser-responsive neurons were more common in the I category, whereas those of laser nonresponsive neurons were more common in the NG category. Therefore neuronal spike trains in the I category may mediate shifts in endogenous or cognitive pain-related behavior. Copyright © 2009 the American Physiological Society

Ghilardi, M. Felice; Moisello, Clara; Silvestri, Giulia; Ghez, Claude; Krakauer, John W.

doi: 10.1152/jn.01138.2007pmid: 19073794

Abstract The ability to perform accurate sequential movements is essential to normal motor function. Learning a sequential motor behavior is comprised of two basic components: explicit identification of the order in which the sequence elements should be performed and implicit acquisition of spatial accuracy for each element. Here we investigated the time course of learning of these components for a first sequence (SEQA) and their susceptibility to interference from learning a second sequence (SEQB). We assessed explicit learning with a discrete index, the number of correct anticipatory movements, and implicit learning with a continuous variable, spatial error, which decreased during learning without subject awareness. Spatial accuracy to individual sequence elements reached asymptotic levels only when the whole sequence order was known. Interference with recall of the order of SEQA persisted even when SEQB was learned 24 h after SEQA. However, there was resistance to interference by SEQB with increased initial training with SEQA. For implicit learning of spatial accuracy, SEQB interfered at 5 min but not 24 h after SEQA. As in the case of sequence order, prolonged initial training with SEQA induced resistance to interference by SEQB. We conclude that explicit sequence learning is more susceptible to anterograde interference and implicit sequence learning is more susceptible to retrograde interference. However, both become resistant to interference with saturation training. We propose that an essential feature of motor skill learning is the process by which discrete explicit task elements are combined with continuous implicit features of movement to form flawless sequential actions. Footnotes Copyright © 2009 the American Physiological Society

Ma, Li-Qun; Liu, Chao; Wang, Fang; Xie, Na; Gu, Jun; Fu, Hui; Wang, Jiang-Hua; Cai, Fei; Liu, Jue; Chen, Jian-Guo

doi: 10.1152/jn.90345.2008pmid: 19225177

Abstract Recent evidences indicate the existence of a putative novel phosphatidylinositol (PI)-linked D 1 dopamine receptor that mediates excellent anti-Parkinsonian but less severe dyskinesia action. To further understand the basic physiological function of this receptor in brain, the effects of a PI-linked D 1 dopamine receptor-selective agonist 6-chloro-7,8-dihydroxy-3-methyl-1-(3-methylphenyl)-2,3,4,5-tetrahydro-1H-3-benzazepine (SKF83959) on high-voltage activated (HVA) Ca 2+ currents in primary cultured striatal neurons were investigated by whole cell patch-clamp technique. The results indicated that stimulation by SKF83959 induced an inhibition of HVA Ca 2+ currents in a dose-dependent manner in substance-P (SP)-immunoreactive striatal neurons. Application of D 1 receptor, but not D 2 , α 1 adrenergic, 5-HT receptor, or cholinoceptor antagonist prevented SKF83959-induced reduction, indicating that a D 1 receptor-mediated event assumed via PI-linked D 1 receptor. SKF83959-induced inhibitory modulation was mediated by activation of phospholipase C (PLC), mobilization of intracellular Ca 2+ stores and activation of calcineurin. Furthermore, the inhibitory effects were attenuated significantly by the L-type calcium channel antagonist nifedipine, suggesting that L-type calcium channels involved in the regulation induced by SKF83959. These findings may help to further understand the functional role of the PI-linked dopamine receptor in brain. Footnotes ↵ * L.-Q. Ma and C. Liu contributed equally to this work. Copyright © 2009 the American Physiological Society

Schreiber, Susanne; Samengo, Inés; Herz, Andreas V.M.

doi: 10.1152/jn.90711.2008pmid: 19193775

Abstract Despite intrinsic noise sources, neurons can generate action potentials with remarkable reliability. This reliability is influenced by the characteristics of sensory or synaptic inputs, such as stimulus frequency. Here we use conductance-based models to study the frequency dependence of reliability in terms of the underlying single-cell properties. We are led to distinguish a mean-driven firing regime , where the stimulus mean is sufficient to elicit continuous firing, and a fluctuation-driven firing regime , where spikes are generated by transient stimulus fluctuations. In the mean-driven regime, the stimulus frequency that induces maximum reliability coincides with the firing rate of the cell, whereas in the fluctuation-driven regime, it is determined by the resonance properties of the subthreshold membrane potential. When the stimulus frequency does not match the optimal frequency, the two firing regimes exhibit different “symptoms” of decreased reliability: reduced spike-time precision and reduced spike probability, respectively. As a signature of stochastic resonance, reliable spike generation in the fluctuation-driven regime can benefit from intermediate amounts of noise that boost spike probability without significantly impairing spike-time precision. Our analysis supports the view that neurons are endowed with selection mechanisms that allow only certain stimulus frequencies to induce reliable spiking. By modulating the intrinsic cell properties, the nervous system can thus tune individual neurons to pick out specific input frequency bands with enhanced spike precision or spike probability. Footnotes Copyright © 2009 the American Physiological Society

Strandberg, Joakim; Wasling, Pontus; Gustafsson, Bengt

doi: 10.1152/jn.91210.2008pmid: 19225168

Abstract Brief test-pulse stimulation (0.2–0.05 Hz) of naïve (previously nonstimulated) developing hippocampal CA3–CA1 synapses leads to a substantial synaptic depression, explained by α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) silencing. Using field recordings in hippocampal slices from P8 to P12 rats, we examined this depression of naïve synapses using more prolonged test-pulse stimulation as well as low-frequency (1 Hz) stimulation (LFS). We found that 900 stimuli produced depression during stimulation to ∼40% of the naïve level independent of whether test-pulse stimulation or LFS was used. This result was also observed during combined blockade of N -methyl- d -aspartate/metabotropic glutamate receptors (NMDAR/mGluRs) although the depression was smaller (to ∼55% of naïve level). Using separate blockade of either NMDARs or mGluRs, we found that this impairment of the depression resulted from the NMDAR, and not from the mGluR, blockade. In fact, during NMDAR blockade alone, depression was smaller even than that observed during combined blockade. We also found that mGluR blockade alone facilitated the LFS-induced depression. In conclusion, test-pulse stimulation produced as much depression as LFS when applied to naïve synapses even when allowing for NMDAR and mGluR activation. Our results seem in line with the notion that NMDARs and mGluRs may exert a bidirectional control on AMPA receptor recruitment to synapses. Copyright © 2009 the American Physiological Society

de Rugy, Aymar; Hinder, Mark R.; Woolley, Daniel G.; Carson, Richard G.

doi: 10.1152/jn.90898.2008pmid: 19225174

Abstract Reaching to visual targets engages the nervous system in a series of transformations between sensory information and motor commands. That which remains to be determined is the extent to which the processes that mediate sensorimotor adaptation to novel environments engage neural circuits that represent the required movement in joint-based or muscle-based coordinate systems. We sought to establish the contribution of these alternative representations to the process of visuomotor adaptation. To do so we applied a visuomotor rotation during a center-out isometric torque production task that involved flexion/extension and supination/pronation at the elbow-joint complex. In separate sessions, distinct half-quadrant rotations (i.e., 45°) were applied such that adaptation could be achieved either by only rescaling the individual joint torques (i.e., the visual target and torque target remained in the same quadrant) or by additionally requiring torque reversal at a contributing joint (i.e., the visual target and torque target were in different quadrants). Analysis of the time course of directional errors revealed that the degree of adaptation was lower (by ∼20%) when reversals in the direction of joint torques were required. It has been established previously that in this task space, a transition between supination and pronation requires the engagement of a different set of muscle synergists, whereas in a transition between flexion and extension no such change is required. The additional observation that the initial level of adaptation was lower and the subsequent aftereffects were smaller, for trials that involved a pronation–supination transition than for those that involved a flexion–extension transition, supports the conclusion that the process of adaptation engaged, at least in part, neural circuits that represent the required motor output in a muscle-based coordinate system. Copyright © 2009 the American Physiological Society