Tonic Response Research Articles

Heterogeneity of neuromasts in a fish without lateral line canals: the pufferfish (Takifugu obscurus) model.

Fish detect water motion with their mechanosensory lateral line. The basic functional unit of the lateral line is the neuromast. In most fish species, neuromasts are located in lateral line canals (canal neuromasts) or on the skin (superficial neuromasts). In this paper, we describe the lateral line system of the pufferfish, Takifugu obscurus If threatened, this fish inflates its body by sucking water into the esophagus. Pufferfish lack a canal system but have neuromasts located directly on the skin or in open grooves. Each groove houses tall, medium and short neuromasts, based on the height of their pedestal. One or more medium neuromasts were always located between two tall neuromasts, and the short neuromasts were scattered between them. Tall neuromasts showed phasic responses to water jets, similar to the canal neuromasts of other fish species. In contrast, the medium and short neuromasts showed tonic responses to water jets. The response properties of nerve fibers that innervated the medium and short neuromasts were similar to those of the superficial neuromasts found in other fish species. Our results suggest that each groove of a pufferfish has two functional groups of neuromasts. This may allow pufferfish to extract spatial and temporal hydrodynamic information, despite the changes in body shape that occur during and after inflation. The short neuromasts at the bottom of a groove most likely supplement the medium neuromasts when the body is maximally inflated.

Multiple time courses of somatosensory responses in human cortex

Here we show how anatomical and functional data recorded from patients undergoing stereo-EEG can be used to decompose the cortical processing following nerve stimulation in different stages characterized by specific topography and time course. Tibial, median and trigeminal nerves were stimulated in 96 patients, and the increase in gamma power was evaluated over 11878 cortical sites. All three nerve datasets exhibited similar clusters of time courses: phasic, delayed/prolonged and tonic, which differed in topography, temporal organization and degree of spatial overlap. Strong phasic responses of the three nerves followed the classical somatotopic organization of SI, with no overlap in either time or space. Delayed responses presented overlaps between pairs of body parts in both time and space, and were confined to the dorsal motor cortices. Finally, tonic responses occurred in the perisylvian region including posterior insular cortex and were evoked by the stimulation of all three nerves, lacking any spatial and temporal specificity. These data indicate that the somatosensory processing following nerve stimulation is a multi-stage hierarchical process common to all three nerves, with the different stages likely subserving different functions. While phasic responses represent the neural basis of tactile perception, multi-nerve tonic responses may represent the neural signature of processes sustaining the capacity to become aware of tactile stimuli.

Connections of Anterior Thalamic Visual Centers in the Leopard Frog, Rana pipiens

The amphibian retina projects to two discrete regions of neuropil in the anterior thalamus: the neuropil of Bellonci and the corpus geniculatum. These retinorecipient areas are encompassed within a larger zone of surrounding neuropil we call the NCZ (for neuropil of Bellonci/corpus geniculatum zone). The NCZ is characterized electrophysiologically by a distinctive tonic oscillatory response to blue light; it appears to be a visual module involved in processing the stationary visual environment. Using horseradish peroxidase (HRP), we mapped the connections of the NCZ. Retrogradely labeled cell bodies are found in: (1) the contralateral anterior thalamus; (2) both retinas; and (3) the posterior medial dorsal thalamus (PMDT). Anterogradely labeled fibers are found in: (1) the contralateral anterior thalamus; (2) the ipsilateral PMDT; (3) the ipsilateral neuropil lateral to the posterior tuberculum in the ventrolateral posterior thalamus; and (4) the ipsilateral anterior medulla. There are no direct connections between the NCZ and the telencephalon, the tectum, or the suprachiasmatic nucleus. Applying HRP to the PMDT, we found that its inputs are limited to the contralateral and ipsilateral NCZ and the contralateral PMDT. Thus, PMDT appears to be a satellite of the NCZ. Blue light elicits tonic oscillatory electrical responses in the PMDT quite similar to the responses to blue light in the NCZ. We discuss how the leopard frog NCZ and the mammalian ventral lateral geniculate nucleus share anatomical and physiological properties.

Individual differences in eye blink rate predict both transient and tonic pupil responses during reversal learning.

The pupil response under constant illumination can be used as a marker of cognitive processes. In the past, pupillary responses have been studied in the context of arousal and decision-making. However, recent work involving Parkinson's patients suggested that pupillary responses are additionally affected by reward sensitivity. Here, we build on these findings by examining how pupil responses are modulated by reward and loss while participants (N = 30) performed a Pavlovian reversal learning task. In fast (transient) pupil responses, we observed arousal-based influences on pupil size both during the expectation of upcoming value and the evaluation of unexpected monetary outcomes. Importantly, after incorporating eye blink rate (EBR), a behavioral correlate of striatal dopamine levels, we observed that participants with lower EBR showed stronger pupil dilation during the expectation of upcoming reward. Subsequently, when reward expectations were violated, participants with lower EBR showed stronger pupil responses after experiencing unexpected loss. Across trials, the detection of a reward contingency reversal was reflected in a slow (tonic) dilatory pupil response observed already several trials prior to the behavioral report. Interestingly, EBR correlated positively with this tonic detection response, suggesting that variability in the arousal-based detection response may reflect individual differences in striatal dopaminergic tone. Our results provide evidence that a behavioral marker of baseline striatal dopamine level (EBR) can potentially be used to describe the differential effects of value-based learning in the arousal-based pupil response.

Adaptable interaction between aquaporin-1 and band 3 reveals a potential role of water channel in blood CO2 transport.

Human CO2 respiration requires rapid conversion between CO2 and HCO3- Carbonic anhydrase II facilitates this reversible reaction inside red blood cells, and band 3 [anion exchanger 1 (AE1)] provides a passage for HCO3- flux across the cell membrane. These 2 proteins are core components of the CO2 transport metabolon. Intracellular H2O is necessary for CO2/HCO3- conversion. However, abundantly expressed aquaporin 1 (AQP1) in erythrocytes is thought not to be part of band 3 complexes or the CO2 transport metabolon. To solve this conundrum, we used Förster resonance energy transfer (FRET) measured by fluorescence lifetime imaging (FLIM-FRET) and identified interaction between aquaporin-1 and band 3 at a distance of 8 nm, within the range of dipole-dipole interaction. Notably, their interaction was adaptable to membrane tonicity changes. This suggests that the function of AQP1 in tonicity response could be coupled or correlated to its function in band 3-mediated CO2/HCO3- exchange. By demonstrating AQP1 as a mobile component of the CO2 transport metabolon, our results uncover a potential role of water channel in blood CO2 transport and respiration.-Hsu, K., Lee, T.-Y., Periasamy, A., Kao, F.-J., Li, L.-T., Lin, C.-Y., Lin, H.-J., Lin, M. Adaptable interaction between aquaporin-1 and band 3 reveals a potential role of water channel in blood CO2 transport.

Tonic immobility during sexual assault-a common reaction predicting post-traumatic stress disorder and severe depression.

Active resistance is considered to be the 'normal' reaction during rape. However, studies have indicated that similar to animals, humans exposed to extreme threat may react with a state of involuntary, temporary motor inhibition known as tonic immobility. The aim of the present study was to assess the occurrence of tonic immobility during rape and subsequent post-traumatic stress disorder and severe depression. Tonic immobility at the time of the assault was assessed using the Tonic Immobility Scale in 298 women who had visited the Emergency clinic for raped women within 1month of a sexual assault. Information about the assault and the victim characteristics were taken from the structured clinical data files. After 6months, 189 women were assessed regarding the development of post-traumatic stress disorder and depression. Of the 298 women, 70% reported significant tonic immobility and 48% reported extreme tonic immobility during the assault. Tonic immobility was associated with the development of post-traumatic stress disorder (OR 2.75; 95% CI 1.50-5.03, p=0.001) and severe depression (OR 3.42; 95% CI 1.51-7.72, p=0.003) at 6months. Further, previous trauma history (OR 2.36; 95% CI 1.48-3.77, p<0.001) and psychiatric treatment history (OR 2.00; 95% CI 1.26-3.19, p=0.003) were associated with the tonic immobility response. Tonic immobility during rape is a common reaction associated with subsequent post-traumatic stress disorder and severe depression. Knowledge of this reaction in sexual assault victims is important in legal matters and for healthcare follow up.

Asymmetries between convergence and divergence reveal tonic vergence is dependent upon phasic vergence function.

Horizontal vergence eye movements are controlled by two processes, phasic and slow-tonic. Slow-tonic responses are hypothesized to be stimulated by the faster, pulse-step neural output of the phasic system. This suggests that the general behavior of each system should be similar; however, this relationship has yet to be investigated directly. We characterize the relationship between phasic and tonic vergence by quantifying directional asymmetries in the response properties of each mechanism to the same disparity amplitudes. Four subjects viewed symmetric steps in disparity dichoptically at 40 cm while eye movements were recorded with infrared oculography. First- and second-order phasic and slow-tonic convergence response properties increased linearly with disparity demand (p < 0.01), whereas divergence responses did not (p > 0.05). Phasic divergence responses were slower than convergence (p = 0.012) and were associated with a higher frequency of saccades (p < 0.001). The average rate of slow-tonic change was correlated to the average peak velocity of phasic vergence at the same vergence demand in both directions, r = 0.78, p < 0.0001. Clear directional asymmetries were observed in phasic and tonic vergence responses. The response properties of the slow-tonic mechanism varied directly with the peak velocity of the complementary phasic system. These results provide empirical evidence of the relationship between phasic and slow-tonic vergence, suggesting that the latter depends on the motor function of the former, specifically the peak velocity. The recruitment of additional oculomotor mechanisms, such as saccades, improved the phasic response properties of the slower divergence mechanism but did not directly influence the response behavior of the slow-tonic mechanism.

Phorbol 12,13-dibutyrate–induced protein kinase C activation triggers sustained contracture in human myometrium in vitro

Although physiologic transition from rhythmic contractions to uterine retraction postpartum remains a poorly understood process, it has been shown that the latter is essential in the prevention of hemorrhage and its negative consequences. To investigate the transition from oscillatory contractions to tonic contracture in human myometrium after delivery, a mechanism purported to facilitate postpartum hemostasis. Protein kinase C (PKC) plays a key regulatory role in human uterine contractions because it can prevent dephosphorylation of regulatory proteins and sensitize the contractile machinery to low Ca2+. Thus, activation of PKC by phorbol 12,13-dibutyrate (PDBu) may act as a strong uterotonic agent. Uterine biopsies were obtained from consenting women undergoing elective caesarian delivery at term without labor (N=19). Isometric tension measurements were performed on uterine strips (n= 114). The amplitudes and area under the curve of phasic contractions and tonic responses were measured and compared. A total of 1 μM PDBu was added to the isolated organ baths, and maximal tension of the uterine contracture was determined in the absence and presence ofeither 1 μM of staurosporine, 100 nM nifedipine, or 10 μM cyclopiazonic acid to assess the role of PKC and calcium sensitivity on uterine contractility. On the addition of PDBu on either basal or oxytocin-induced activity, consistent contractures were obtained concomitant with complete inhibition of phasic contractions. After a 30-minute incubation period, the mean amplitude of the PDBu-induced tone represented 65.3% of the amplitude of spontaneous contraction. Staurosporine, a protein kinase inhibitor, induced a 91.9% inhibition of PDBu contractures, a process not affected by nifedipine or cyclopiazonic acid, thus indicating that this mechanism is largely Ca2+ independent. Pharmacologic activation of PKC leads to a significant contracture of the myometrium. Together, these data suggest that the up-regulation of PKC plays a physiologic role in the modulation of uterine contracture after delivery. A switch from phasic to strong tonic contractions potentially may facilitate postpartum hemostasis.

The dependence of the phasic response of the taste nerves on stimulus flow rate arises in the diffusion boundary layer region at the lingual surface: A convective-diffusion analysis

The dynamics of the taste neural response are highly dependent on the velocity of the stimulus solution delivered to the taste receptor cells. In anesthetized rats, stimulus solution delivered at high stimulus flow rate (1 m1/s) to the taste receptor cells on the dorsal lingual surface by axisymmetric stagnation flow yields a neural response with a rapid transient increase above baseline to peak response. At flow cessation (after about 3s) the neural response then rapidly declines exponentially to steady state or tonic response. This rapid transient or phasic response is not observed at low stimulus flow rate (e.g. 7.5ml/min). In the latter case the neural response rises with a slow exponential decline ultimately attaining the same steady state value observed in the high flow rate case. Although the taste quality may be nominally the same in each case, the dynamics of the afferent response differ markedly. Therefore, the input to the brain, where a variety of sensory inputs related to food ingestion are combined to yield a food’s flavor value, is not the same for each flow rate. Thus physical variables at work in the oral cavity, such as flow velocity and viscosity, play a role in determining the palatability of a meal through their effects on both taste and tactile receptors. I show here that stimulus flow rate controls the appearance of a phasic transient neural response by its effect on the thickness of the diffusion boundary layer in contact with the dorsal lingual surface. This is accomplished by solving the convective-diffusion equation with the normal component of the stimulus flow velocity determined by stagnation flow fluid dynamics. In so doing I derive useful approximate closed form solutions for both planar and axisymmetric stagnation flow. I propose a mathematical model of taste receptor function that depends on the surface concentration of the taste stimulus. I show that the surface stimulus concentration (and therefore the neural response) increases with fluid velocity and that the thickness of the diffusion boundary layer is inversely proportional to the square-root of stimulus fluid velocity. A phasic transient neural response emerges at high flow rates because the surface stimulus concentration initially rises rapidly and then subsequently declines as the system evolves through a succession of steady states of diminishing fluid velocity. The model also accounts for diminished taste responses observed with increased stimulus solution viscosity.

Emergency braking is affected by the use of cruise control

ABSTRACTObjective: We compared the differences in the braking response to vehicle collision between an active human emergency braking (control condition) and cruise control (CC) or adaptive cruise control (ACC).Methods: In 11 male subjects, age 22 to 67 years, we measured the active emergency braking response during manual driving using the accelerator pedal (control condition) or in condition mimicking CC or ACC. In both conditions, we measured the brake reaction time (BRT), delay to produce the peak braking force (PBD), total emergency braking response (BRT + PBD), and peak braking force (PBF). Electromyograms of leg and thigh muscles were recorded during braking. The tonic vibratory response (TVR), Hoffman reflex (HR), and M-waves were recorded in leg muscles to explore the change in sensorimotor control.Results: No difference in PBF, TVR amplitude, HR latency, and Hmax/Mmax ratio were found between the control and CC/ACC conditions. On the other hand, BRT and PBD were significantly lengthened in the CC/ACC condition (240 ± 13 ms and 704 ± 70 ms, respectively) compared to control (183 ± 7 ms and 568 ± 36 ms, respectively). BRT increased with the age of participants and the driving experience shortened PBD and increased PBF.Conclusions: In male subjects, driving in a CC/ACC condition significantly delays the active emergency braking response to vehicle collision. This could result from higher amplitude of leg motion in the CC/ACC condition and/or by the age-related changes in motor control. Car and truck drivers must take account of the significant increase in the braking distance in a CC/ACC condition.

Neurotransmitter-Regulated Regeneration in the Zebrafish Retina.

SummaryCurrent efforts to repair damaged or diseased mammalian retinas are inefficient and largely incapable of fully restoring vision. Conversely, the zebrafish retina is capable of spontaneous regeneration upon damage using Müller glia (MG)-derived progenitors. Understanding how zebrafish MG initiate regeneration may help develop new treatments that prompt mammalian retinas to regenerate. We show that inhibition of γ-aminobutyric acid (GABA) signaling facilitates initiation of MG proliferation. GABA levels decrease following damage, and MG are positioned to detect decreased ambient levels and undergo dedifferentiation. Using pharmacological and genetic approaches, we demonstrate that GABAA receptor inhibition stimulates regeneration in undamaged retinas while activation inhibits regeneration in damaged retinas.

The Bimodal Nature of Neurovascular Coupling: Slow Tonic and Rapid Phasic Responses are Separately Controlled by Specific Astrocyte Metabotropic and Ionotropic Glutamate Receptors

Neurons, by virtue of their complex and continuously changing signaling roles in brain, must be able to regulate access to energy in order to maintain their ability to communicate meaningful frequency-encoded information. This is accomplished by release of neurotransmitters to astrocytes that in turn signal the vascular system to increase cerebral blood flow (CBF). This process has been termed “neurovascular coupling” (NVC). It has also been observed that NVC is bimodal in that there are two separate mechanisms for control of CBF. One type is rapid [phasic] in response to changes in glutamatergic synaptic activity and release of glutamate (Glu), K+ and nitric oxide (NO). Uptake of Glu and K+ by astrocytes induces Ca2+ waves activating regional astrocyte syncytium have to liberate prostaglandins which in turn dilate capillaries by relaxing surrounding pericytes. The NO dilates arterioles by relaxing surrounding smooth muscle cells. These agents acting in concert sharply increase CBF within 1-3 seconds. The other type is slow [tonic] reflecting ongoing neuronal metabolic activity of all neuron types independent of changes in synaptic activity or astrocyte Ca2+ waves and eliciting modest oscillations in CBF in 10’s of seconds. In this review, we describe two neuronal signaling mechanisms that match the criteria for phasic and for tonic regulation of CBF. The difference is being the nature and source of the “Glu” released and of their targeted astrocyte receptors. Dependence on synaptic activity limits phasic responses to gray matter, but tonic responses can regulate CBF in both gray matter and white matter and may be the primary regulator of CBF in white matter.

Bioassay-directed isolation of falcarindiol and isoacetovanillon from Pycnocycla caespitosa based on KCl-induced contraction in rat uterus smooth muscles.

Hydroalcoholic extract and essential oil of aerial parts of Pycnocycla caespitosa have spasmolytic activity on rat ileum contractions. The objective of this research was to separate fractions of total hydroalcoholic extract of P. caespitosa guided by their spasmolytic activity on rat uterus. Aerial parts of P. caespitosa were extracted with ethanol. The concentrated extract was subjected to column chromatography and thin layer chromatography (TLC) for isolation fractions, then one of the bioactive fractions was subjected to further isolation to find its active components. Five fractions were obtained (Fr.1-Fr.5) and their anti-spasmodic activities were examined on uterus contraction induced by KCl (80 mM) and compared with ritodrine. In addition, spasmolytic effect of Fr.4 (one of the bioactive fractions) was determined on rat uterus induced by oxytocin (0.0005 IU/mL) and compared with ritodrine. Hydroalcoholic extract of P. caespitosa (0.032-2 mg/mL) reduced the responses to KCl but the inhibitory effect was not complete with 2 mg/mL extract in the bath. Four fractions (Fr.1, Fr.2, Fr.3 and Fr.4) (32-500 μg/mL) inhibited rat uterus contractions on the uterus while Fr.4 was slightly more active than others (IC50 = 146 ± 23 μg/mL). Falcarindiol and isoacetovanillone were identified from Fr.4 using phytochemical methods including high-performance liquid chromatography (HPLC), nuclear magnetic resonance (NMR) and TLC. In conclusion, in this research bioactivity guided technique was successfully used for separation of active fraction of P. caespitosa. Falcarindiol and isoacetovanillone were identified from the active fraction which inhibited both tonic and rhythmic contractile responses in rat isolated uterus.

Recognizing the Common Origins of Dystonia and the Development of Human Movement: A Manifesto of Unmet Needs in Isolated Childhood Dystonias.

Dystonia in childhood may be severely disabling and often unremitting and unrecognized. Considered a rare disorder, dystonic symptoms in childhood are pervasive in many conditions including disorders of developmental delay, cerebral palsy (CP), autism, neurometabolic, neuroinflammatory, and neurogenetic disorders. Collectively, there is a need to recognize the role of early postures and movements which characterize phases of normal fetal, infant, and child development as a backdrop to the many facets of dystonia in early childhood neurological disorders and to be aware of the developmental context of dystonic symptoms. The role of cocontraction is explored throughout infancy, childhood, young adulthood, and in the elderly. Under-recognition of pervasive dystonic disorders of childhood, including within CP is reviewed. Original descriptions of CP by Gowers are reviewed and contemporary physiological demonstrations are used to illustrate support for an interpretation of the tonic labyrinthine response as a manifestation of dystonia. Early recognition and molecular diagnosis of childhood dystonia where possible are desirable for appropriate clinical stratification and future precision medicine and functional neurosurgery where appropriate. A developmental neurobiological perspective could also be useful in exploring new clinical strategies for adult-onset dystonia disorders focusing on environmental and molecular interactions and systems behaviors.

The impact of luminance on tonic and phasic pupillary responses to sustained cognitive load

Pupillary reactions independent of light conditions have been linked to cognition for a long time. However, the light conditions can impact the cognitive pupillary reaction. Previous studies underlined the impact of luminance on pupillary reaction, but it is still unclear how luminance modulates the sustained and transient components of pupillary reaction – tonic pupil diameter and phasic pupil response. In the present study, we investigated the impact of the luminance on these two components under sustained cognitive load. Fourteen participants performed a novel working memory task combining mathematical computations with a classic n-back task. We studied both tonic pupil diameter and phasic pupil response under low (1-back) and high (2-back) working memory load and two luminance levels (gray and white). We found that the impact of working memory load on the tonic pupil diameter was modulated by the level of luminance, the increase in tonic pupil diameter with the load being larger under lower luminance. In contrast, the smaller phasic pupil response found under high load remained unaffected by luminance. These results showed that luminance impacts the cognitive pupillary reaction – tonic pupil diameter (phasic pupil response) being modulated under sustained (respectively, transient) cognitive load. These findings also support the relationship between the locus-coeruleus system, presumably functioning in two firing modes – tonic and phasic – and the pupil diameter. We suggest that the tonic pupil diameter tracks the tonic activity of the locus-coeruleus while phasic pupil response reflects its phasic activity. Besides, the designed novel cognitive paradigm allows the simultaneous manipulation of sustained and transient components of the cognitive load and is useful for dissociating the effects on the tonic pupil diameter and phasic pupil response.

An improved approach for measuring the tonic stretch reflex response of spastic muscles

We propose a new method for detecting the onset of the stretch reflex response for assessment of spasticity based on the Tonic Stretch Reflex Threshold (TSRT). Our strategy relies on a three-stage approach to detect the onset of the reflex EMG activity: (i) Reduction of baseline activity by means of Empirical Mode Decomposition; (ii) Extraction of the complex envelope of the EMG signal by means of Hilbert Transform (HT) and; iii) A double threshold decision rule. Simulated and real EMG data were used to evaluate and compare our method (TSRT-EHD) against three other popular methods described in the literature to assess TSRT (‘Kim’, ‘Ferreira’ and ‘Blanchette’). Four different groups of signals containing simulated evoked stretch reflex EMG activities were generated: groups A and B without spontaneous EMG activity at rest and signal-to-noise ratio (SNR) of 10dB and 20dB respectively; groups C and D with spontaneous EMG activity at rest, as observed frequently in spastic muscles, and SNR of 10dB and 20dB respectively. The results with simulated data showed a significantly higher accuracy of TSRT-EHD for detecting the onset of the reflex EMG activity in groups C and D when compared to the other methods. Analyses using real data from five post stroke spastic subjects demonstrated that the TSRTs generated by each method were dramatically different from one another. Nevertheless, only TSRT-EHD provided valid measures across all subjects.

Reward and Behavioral Factors Contributing to the Tonic Activity of Monkey Pedunculopontine Tegmental Nucleus Neurons during Saccade Tasks.

The pedunculopontine tegmental nucleus (PPTg) in the brainstem plays a role in controlling reinforcement learning and executing conditioned behavior. We previously examined the activity of PPTg neurons in monkeys during a reward-conditioned, visually guided saccade task, and reported that a population of these neurons exhibited tonic responses throughout the task period. These tonic responses might depend on prediction of the upcoming reward, successful execution of the task, or both. Here, we sought to further distinguish these factors and to investigate how each contributes to the tonic neuronal activity of the PPTg. In our normal visually guided saccade task, the monkey initially fixated on the central fixation target (FT), then made saccades to the peripheral saccade target and received a juice reward after the saccade target disappeared. Most of the tonic activity terminated shortly after the reward delivery, when the monkey broke fixation. To distinguish between reward and behavioral epochs, we then changed the task sequence for a block of trials, such that the saccade target remained visible after the reward delivery. Under these visible conditions, the monkeys tended to continue fixating on the saccade target even after the reward delivery. Therefore, the prediction of the upcoming reward and the end of an individual trial were separated in time. Regardless of the task conditions, half of the tonically active PPTg neurons terminated their activity around the time of the reward delivery, consistent with the view that PPTg neurons might send reward prediction signals until the time of reward delivery, which is essential for computing reward prediction error in reinforcement learning. On the other hand, the other half of the tonically active PPTg neurons changed their activity dependent on the task condition. In the normal condition, the tonic responses terminated around the time of the reward delivery, while in the visible condition, the activity continued until the disappearance of the saccade target (ST) after reward delivery. Thus, for these neurons, the tonic activity might be related to maintaining attention to complete fixation behavior. These results suggest that, in addition to the reward value information, some PPTg neurons might contribute to the execution of conditioned task behavior.

To see or not to see; the ability of the magno- and parvocellular response to manifest itself in the VEP determines its appearance to a pattern reversing and pattern onset stimulus.

IntroductionThe relationship between stimulus property, brain activity, and the VEP is still a matter of uncertainty.MethodWe recorded the VEP of 43 volunteers when viewing a series of dartboard images presented as both a pattern reversing and pattern onset/offset stimulus. Across the dartboard images, the total stimulus area undergoing a luminance contrast change was varied in a graded manner.ResultsWe confirmed the presence of two independent neural processing stages. The amplitude of VEP components across our pattern reversing stimuli signaled a phasic neural response based on a temporal luminance contrast selective mechanism. The amplitude of VEP components across the pattern onset stimuli signaled both a phasic and a tonic neural response based on a temporal‐ and spatial luminance contrast selective mechanism respectively. Oscillation frequencies in the VEP suggested modulation of the phasic neural response by feedback from areas of the dorsal stream, while feedback from areas of the ventral stream modulated the tonic neural response. Each processing stage generated a sink and source phase in the VEP. Source localization indicated that during the sink phase electric current density was highest in V1, while during the source phase electric current density was highest in extra‐striate cortex. Our model successfully predicted the appearance of the VEP to our images whether presented as a pattern reversing or a pattern onset/offset stimulus.ConclusionsFocussing on the effects of a phasic and tonic response rather than contrast response function on the VEP, enabled us to develop a theory linking stimulus property, neural activity and the VEP.

Dynamic Regulation of the GABAA Receptor Function by Redox Mechanisms.

Oxidizing and reducing agents, which are currently involved in cell metabolism and signaling pathways, can regulate fast inhibitory neurotransmission mediated by GABA receptors in the nervous system. A number of in vitro studies have shown that diverse redox compounds, including redox metabolites and reactive oxygen and nitrogen species, modulate phasic and tonic responses mediated by neuronal GABAA receptors through both presynaptic and postsynaptic mechanisms. We review experimental data showing that many redox agents, which are normally present in neurons and glia or are endogenously generated in these cells under physiologic states or during oxidative stress (e.g., hydrogen peroxide, superoxide and hydroxyl radicals, nitric oxide, ascorbic acid, and glutathione), induce potentiating or inhibiting actions on different native and recombinant GABAA receptor subtypes. Based on these results, it is thought that redox signaling might represent a homeostatic mechanism that regulates the function of synaptic and extrasynaptic GABAA receptors in physiologic and pathologic conditions.

Consequences of simulated car driving at constant high speed on the sensorimotor control of leg muscles and the braking response.

Due to the increase in time spent seated in cars, there is a risk of fatigue of the leg muscles which adjust the force exerted on the accelerator pedal. Any change in their sensorimotor control could lengthen the response to emergency braking. Fourteen healthy male subjects (mean age: 42±4 years) were explored. Before and after a 1-h driving trial at 120km h-1 , we measured the braking response, the maximal leg extension and foot inversion forces, the tonic vibratory response (TVR) in gastrocnemius medialis (GM) and tibialis anterior (TA) muscles to explore the myotaticreflex, and the Hoffmann reflex (H-reflex). During driving, surface electromyograms (EMGs) of GM and TA were recorded and the ratio between high (H) andlow (L) EMG energies allowed to evaluate the recruitment of high- and low-frequency motor unit discharges. During driving, the H/L ratio decreased in TA, whereas modest and often no significant H/L changes occurred in GM muscle. After driving, the maximal foot inversion force decreased (-19%), while the leg extension force did not vary. Reduced TVR amplitude (-29%) was measured in TA, but no H-reflex changes were noted. The braking reaction time was not modified after the driving trial. Driving at constant elevated speed reduced the myotatic reflex and the recruitment of motor units in TA muscle. The corresponding changes were rarely present in the GM muscle that plays a key role in the braking response, and this could explain the absence of a reduced braking reaction time.