On the non-adrenergic,non-cholinergic contribution to the parasympathetic nerve-evoked secretion of parotid saliva in the rat

A secretion of parotid saliva in the anaesthetized rat in response to stimulation of the parasympathetic nerve occurs in the presence of atropine and adrenoceptor antagonists, albeit reduced and transient in the face of continuous high-frequency stimulation (40 Hz). In non-atropinized rats prolonged stimulation of the parasympathetic nerve at a high frequency (40 Hz, 40 min), aiming at depletion of the neuronal stores of transmitters thought to be responsible for the non-adrenergic, non-cholinergic (NANC) secretion of parotid saliva, was performed. The magnitude of the secretory response to various stimulation frequencies (0.2–60 Hz) applied to the parasympathetic nerve was assessed before and after the period of high-frequency stimulation. The second time, the frequency-response curve was shifted to the right and, moreover, the initial maximal secretory response was not reached. Control experiments suggested that this reduction in secretory responses could be attributed neither to impaired cholinergic neurotransmission nor to decreased responsiveness of the secretory cells. The secretory responses to parasympathetic nerve stimulation after high-frequency stimulation are thought to be evoked by acetylcholine predominantly. When these responses were compared with (1) those obtained before high-frequency stimulation and thought to be evoked by acetylcholine and non-adrenergic, non-cholinergic transmitters in conjunction and (2) those depending on non-adrenergic, non-cholinergic transmitters only it appears that the non-adrenergic, non-cholinergic transmission contributes to the parasympathetic secretory response at a frequency (0.2 Hz) far below threshold frequency (5 Hz) for the non adrenergic, non-cholinergic evoked secretory response. At frequencies below 20 Hz it appears that acetylcholine and non-adrenergic, non-cholinergic transmitters interact positively thereby enhancing the secretory responses.     

On the non-adrenergic, non-cholinergic contribution to the parasympathetic nerve-evoked secretion of parotid saliva in the rat.

A secretion of parotid saliva in the anaesthetized rat in response to stimulation of the parasympathetic nerve occurs in the presence of atropine and adrenoceptor antagonists, albeit reduced and transient in the face of continuous high-frequency stimulation (40 Hz). In non-atropinized rats prolonged stimulation of the parasympathetic nerve at a high frequency (40 Hz, 40 min), aiming at depletion of the neuronal stores of transmitters thought to be responsible for the non-adrenergic, non-cholinergic (NANC) secretion of parotid saliva, was performed. The magnitude of the secretory response to various stimulation frequencies (0.2-60 Hz) applied to the parasympathetic nerve was assessed before and after the period of high-frequency stimulation. The second time, the frequency-response curve was shifted to the right and, moreover, the initial maximal secretory response was not reached. Control experiments suggested that this reduction in secretory responses could be attributed neither to impaired cholinergic neurotransmission nor to decreased responsiveness of the secretory cells. The secretory responses to parasympathetic nerve stimulation after high-frequency stimulation are thought to be evoked by acetylcholine predominantly. When these responses were compared with (1) those obtained before high-frequency stimulation and thought to be evoked by acetylcholine and non-adrenergic, non-cholinergic transmitters in conjunction and (2) those depending on non-adrenergic, non-cholinergic transmitters only it appears that the non-adrenergic, non-cholinergic transmission contributes to the parasympathetic secretory response at a frequency (0.2 Hz) far below threshold frequency (5 Hz) for the non adrenergic, non-cholinergic evoked secretory response. At frequencies below 20 Hz it appears that acetylcholine and non-adrenergic, non-cholinergic transmitters interact positively thereby enhancing the secretory responses.     

Flashed pattern-induced activity in the visual system: I. The short latency evoked response recorded from the cat visual cortex

Previous methods for estimating visual acuity have used the visual evoked response conventionally the late visual evoked response components or the steady-state potential. The present experiments were undertaken to evaluate the possible use of short latency flashed pattern evoked responses in estimating pattern dependent activity in the cat visual system. Recordings were made from the skull bone and the dura above the primary visual cortex and intracortically. The visual evoked responses to patterned (checks) and non-patterned light flashes of high intensity and short duration were recorded. The visual evoked response activity recorded from the cortical surface had an onset latency of 14–15 ms. The initial positive-negative potential sequences of the responses were similar for patterned and non-patterned stimuli, however a difference was recorded from 35–40 ms after stimulus. The smallest check size which separated a pattern from a non-pattern VER was in the order of 10 min of arc. The results indicate that the short-latency cortical VER may be used to estimate visual resolution.     

Slow Evoked Cortical Responses to Linear Frequency Ramps of a Continuous Pure Tone

Arlinger , S. D., L. B. Jerlvall , T. Ahrén and E. C. Holmgren . Slow evoked cortical responses to linear frequency ramps of a continuous pure tone. Acta physiol. scand. 1976. 98. 412–424. Slow evoked cortical potentials from ten young normal-hearing subjects have been recorded as responses to linear frequency ramps of a continuous pure tone. Frequency changes from 10 to 500 Hz were studied; the rate of frequency change was varied from 0.02 to 50 kHz/s while the duration of the change was varied from 10 to 500 ms. The rate of frequency change was shown to have the greatest bearing on the responses except for frequency ramp durations below 50 ms and frequency changes below 50 Hz. The base frequencies (250–4000 Hz) and sound levels (20–80 dB HL) exerted an influence on the evoked responses that was qualitatively similar to their influence on behavioral thresholds. The direction of the frequency sweep had no significant influence on the evoked responses. A functional model is proposed in which the time derivate of the signal frequency is integrated with an adaptable integration time that is controlled by the rate of the frequency change.     

Hazardous nature of high-temporal-frequency strobe light stimulation: neural mechanisms revealed by magnetoencephalography

Individuals in contemporary society are continually exposed to various visual stimuli. Such stimulation, especially when high in temporal frequency, may sometimes cause unexpected events such as photosensitive seizures. Although many studies have demonstrated that high-temporal-frequency (>3 Hz) visual stimulation can yield hazardous responses in the CNS, the mechanisms by which it does so are still unclear. We therefore investigated the mechanisms of neural perturbation by high-temporal-frequency strobe light stimulation with high-temporal-frequency resolution (4–20 Hz with an interval of 2 Hz) using magnetoencephalography with high temporal and spatial resolution. We show that (1) three temporal dipole phases (phases 1, 2 and 3, by time course) can be identified in the visual evoked magnetic fields (VEF's) across stimulation frequencies based on the goodness-of-fit values for equivalent current dipole estimation and horizontal dipole directions, (2) the dipole moment of VEF's is correlated with autonomic nervous system activity in phases 1 and 2, (3) some temporal stimulation frequencies enhance magnetic responses in phases 1, 2 and 3, and (4) these frequencies are harmonically related, with a greatest common divisor frequency (fundamental frequency) of approximately 6.5 Hz. Our clarification of the temporal frequency characteristics of VEF's will contribute to understanding of the potential hazardous effects of high-temporal-frequency strobe light stimulation in the CNS.     

Non-linearities in response properties of insect visual cells: an analysis in time and frequency domain

Intracellularly recorded voltage responses of the visual cells of the blowfly (Calliphora erythrocephala) were analysed in the time and frequency domains. The photoreceptors were stimulated with pulse (impulse), sine, sine-sweep and pseudorandomly (white noise) modulated green light. The blowfly photoreceptor responses, as analysed from the linear transfer functions, seem to arise from a system similar to that of cascaded low-pass filters, with a corner frequency at about 63 Hz (SD +/- 12 Hz). The system is likely to have at least five poles, including one linear second order term, and a pure delay element. Arising from the non-linearities a second harmonic can be seen in the power spectra of responses elicited by sine modulated light. This non-linearity is at least partly explained by the self-shunting property of the membrane voltage response. Light adaptation increases the non-linearities in frequencies lower than 20 Hz, as seen in the decrease of the coherence function with the signal-to-noise ratio remaining constant. Light adaptation also accelerates the transduction process and it appears in the linear transfer function in a form typical to negative feedback. With low stimulus frequencies it causes a 'phase lead'-type non-linearity. In addition, the sine-sweep responses show quite different frequency characteristics in respect of depolarization and repolarization. Lateral inhibition between photoreceptor responses recorded from retinular cell axons in the lamina appears as a drop in gain and as an increasing phase-lag in frequencies from 30 Hz upwards in linear transfer functions. The source of this capacitive-like coupling can be considered to be in the high resistance barriers compartmentalizing the second optic ganglion into discrete anatomical units.     

Otolith-visual interaction in the control of eye movement produced by sinusoidal vertical linear acceleration in alert cats

Summary 1. Eye movement responses were examined in alert cats during sinusoidal vertical linear acceleration. Stimulus frequencies of 0.20–0.85 Hz with a constant amplitude of 10.5 cm (corresponding to 0.02–0.31 g) were used. A random visual pattern was presented to give sinusoidal vertical optokinetic stimuli of similar amplitude and frequency to the up-down motion of the cat. 2. Sinusoidal linear acceleration in the presence of a stationary visual pattern produced robust eye movement responses with near compensatory phase at all stimulus frequencies tested. With both eyes covered, a vertical linear vestibulo-ocular reflex (LVOR) was frequently produced at a stimulus strength corresponding to 0.04–0.31 g. The evoked LVOR was always small, and the overall mean response phase values advanced by as much as 70 ° at frequencies below 0.56 Hz, indicating that the otolith signals activated by sinusoidal linear acceleration were not, by themselves, converted into compensatory eye position signals under these experimental conditions. 3. Optokinetic stimulation alone produced more lag of response phase as stimulus frequency increased, and the gain of evoked eye movement responses was smaller at higher stimulus frequencies compared to the gain during linear acceleration in the light. Bilateral labyrinthectomies resulted in a significant change of the eye movement responses during linear acceleration when visual inputs were allowed: there was more phase lag at higher stimulus frequencies and a decreased gain at all frequencies tested. These results indicate that the interaction of otolith and visual inputs produces robust eye movement responses with near compensatory phase during sinusoidal linear acceleration in the light.     

Visual Evoked Responses as a Function of Light Intensity in Down''s Syndrome and Nonretarded Subjects

Occipital and central averaged visual evoked responses (VERs) were recorded from nonretarded and Down's syndrome (DS) subjects. Three different light intensities were used, all below levels of stimulation used in previous studies. Overall results showed that DS subjects had significantly larger VER perimeters and longer VER latencies, while nonretarded subjects had significant VER asymmetry in the occipital recording (left> right) at all three intensities, DS subjects showed a significantly greater increase in perimeter scores as a function of intensity, with the widest group separation occurring at the highest level of stimulation (43 phots). However, when VER latencies were measured, the widest group separation occurred at the lowest level of stimulation (0.43) phots. Moreover, the only evidence reported thus far for evoked response asymmetry in DS subjects occurred at the lowest light level, These results illustrate the importance of stimulus parameters in evoked potential studies of mental retardation.     

Tuning of the ocular vestibular evoked myogenic potential (oVEMP) to AC sound shows two separate peaks

The ocular vestibular evoked myogenic potential (oVEMP) is a relatively new method used to assess otolith-ocular pathways in humans. When elicited using air-conducted (AC) sound stimulation, the oVEMP is thought to reflect mostly saccular activation. However, it has been recently suggested that utricular afferents may also contribute to the AC evoked oVEMP. While previous frequency tuning studies of the AC evoked oVEMP report predominately high frequency sensitivity (>400 Hz), few have included the lower frequencies (<200 Hz) at which it has been proposed the utricle is most sensitive. In this study, ten normal subjects were stimulated with AC sound delivered unilaterally using headphones over frequencies from 50 to 1,200 Hz at a near constant A-weighted intensity of 120 dB peak sound pressure level. For AC stimulation, the oVEMP demonstrated maximum amplitudes around 600 Hz, with a second, smaller peak occurring around 100 Hz. The AC evoked oVEMP tuning has two peaks, a dominant one consistent with excitation of the saccule and a smaller one consistent with excitation of the utricle.     

稳态视觉诱发电位频率响应特性研究

目的稳态视觉诱发电位(steady-state visual evoked potential,SSVEP)是大脑对周期性视觉刺激产生的响应,已广泛应用于基于脑电(electroencephalogram,EEG)的脑-机接口(brain-computer interface,BCI)。SSVEP频率响应曲线通常是以发光二极管(light emitting diode,LED)作为视觉刺激器的方式获得的。近年来,计算机显示器广泛用于产生闪烁刺激,然而基于计算机显示器的SSVEP频率响应曲线少有研究。为此,本文研究了基于计算机显示器的SSVEP频率响应特性。方法利用采样正弦编码方法在普通LCD显示器上产生了42个刺激频率(频率范围4~45 Hz),并收集了10位健康受试者的脑电数据,以研究SSVEP幅值/信噪比(signal-to-noise ratio,SNR)与刺激频率的关系。结果较强SSVEP响应出现在大脑枕区。SSVEP基频幅值的峰值出现在10 Hz处,且第二峰值出现在20 Hz处。SSVEP二次谐波幅值的峰值出现在6 Hz且在高刺激频率处幅值较小。低、中频段的SSVEP基频信噪比处于相当的水平。结论本文的实验结果可以为基于计算机显示器的SSVEP-BCIs的频率选择提供依据。     

Functional development of the visual system in normal and protein-deprived rats. IX. Visual evoked response in young rats

Changes in latencies of the visual evoked response (VER) during early post-natal development were examined in protein-deprived (PD) rats. The evoked response to light-flash stimulation was recorded in the dorsal lateral geniculate nucleus (dLGN) and on the surface of the visual cortex. In control rats, latencies of the cortical VER decreased rapidly up to 20 days and slowly thereafter. In PD rats, the latencies of the cortical VER were increased by 10-15 ms at 17 days; the developmental decrease was delayed by approximately 3 days. After 20 days, PD rats also went into a phase with slow decrease of the latencies, and the onset latency of the cortical VER was still increased by some 10 ms at 26/27 days. At this age, PD rats showed an increase in the latencies of the VER in the dLGN which was of similar magnitude to that in the cortical VER, indicating that alterations were more marked in the peripheral parts of the visual system at this stage of development. The findings are in agreement with previous studies indicating that there is a delay of visual system development in PD rats before 20 days. A maturational event which turns rapid into slow development at approximately 20 days in both C and PD rats turns this delay into a distortion of development. The delays and distortions of visual system development may be one causative factor for the functional deficit present in the visual cortex of adult PD rats.     

Frequency-selective augmenting responses by short-term synaptic depression in cat neocortex

Thalamic stimulation at frequencies between 5 and 15 Hz elicits incremental or 'augmenting' cortical responses. Augmenting responses can also be evoked in cortical slices and isolated cortical slabs in vivo . Here we show that a realistic network model of cortical pyramidal cells and interneurones including short-term plasticity of inhibitory and excitatory synapses replicates the main features of augmenting responses as obtained in isolated slabs in vivo . Repetitive stimulation of synaptic inputs at frequencies around 10 Hz produced postsynaptic potentials that grew in size and carried an increasing number of action potentials resulting from the depression of inhibitory synaptic currents. Frequency selectivity was obtained through the relatively weak depression of inhibitory synapses at low frequencies, and strong depression of excitatory synapses together with activation of a calcium-activated potassium current at high frequencies. This network resonance is a consequence of short-term synaptic plasticity in a network of neurones without intrinsic resonances. These results suggest that short-term plasticity of cortical synapses could shape the dynamics of synchronized oscillations in the brain.     

Tracking evoked responses to auditory and visual stimuli in fetuses exposed to maternal high‐risk conditions

Magnetoencephalography (MEG) has been successfully applied to record fetal auditory (auditory evoked response [AER]) and visual evoked responses (VER). In this study, we report the AER and VER development trajectory by tracking the evoked response detectability and latency from recordings starting at 27 weeks of gestation in pregnancies classified as high risk. Fetal MEG and ultrasound recordings were performed on 158 pregnant women, and the total number of fetal auditory and visual tests conducted was 321 and 237, respectively. The overall evoked response analysis showed 237 AER (73.8%) and 164 VER detections (69.2%). The mean AER latency was 290.7 (SD 125.5) ms and the mean VER latency was 293.7 (SD 114.5) ms. The rate of decrease (95% confidence limits) in average AER and VER first‐peak latency between 100–350 ms was 1.97 (?1.86, +5.81) ms/week and 1.35 (?3.83, +6.53) ms/week, respectively. This trend in high‐risk fetuses conforms to the general trajectory of decrease in latency with gestational age progression, even though this decrease was non‐significant, as reported in the case of normal growing fetuses. Although there was a significant difference in detection rates between male and female fetuses, this was not reflected in either latency values or the sensory modality applied. Furthermore, the main factors that had the most significant effect on response detectability included the presence of intervening layers of adipose tissue between the fetal head and stimulus source and an increase in the maternal body mass index.     

Functional coupling of the stabilizing eye and head reflexes during horizontal and vertical linear motion in the cat

Summary The otolith contribution and otolith-visual interaction in eye and head stabilization were investigated in alert cats submitted to sinusoidal linear accelerations in three defined directions of space: up-down (Z motion), left-right (Y motion), and forward-back (X motion). Otolith stimulation alone was performed in total darkness with stimulus frequency varying from 0.05 to 1.39 Hz at a constant half peak-to-peak amplitude of 0.145 m (corresponding acceleration range 0.0014–1.13 g) Optokinetic stimuli were provided by sinusoidally moving a pseudorandom visual pattern in the Z and Y directions, using a similar half peak-to-peak amplitude (0.145 m, i.e., 16.1°) in the 0.025–1.39 Hz frequency domain (corresponding velocity range 2.5°–141°/s). Congruent otolith-visual interaction (costimulation, CS) was produced by moving the cat in front of the earth-stationary visual pattern, while conflicting interaction was obtained by suppressing all visual motion cues during linear motion (visual stabilization method, VS, with cat and visual pattern moving together, in phase). Electromyographic (EMG) activity of antagonist neck extensor (splenius capitis) and flexor (longus capitis) muscles as well as horizontal and vertical eye movements (electrooculography, EOG) were recorded in these different experimental conditions. Results showed that otolith-neck (ONR) and otolith-ocular (OOR) responses were produced during pure otolith stimulation with relatively weak stimuli (0.036 g) in all directions tested. Both EMG and EOG response gain slightly increased, while response phase lead decreased (with respect to stimulus velocity) as stimulus frequency increased in the range 0.25–1.39 Hz. Otolith contribution to compensatory eye and neck responses increased with stimulus frequency, leading to EMG and EOG responses, which oppose the imposed displacement more and more. But the otolith system alone remained unable to produce perfect compensatory responses, even at the highest frequency tested. In contrast, optokinetic stimuli in the Z and Y directions evoked consistent and compensatory eye movement responses (OKR) in a lower frequency range (0.025–0.25 Hz). Increasing stimulus frequency induced strong gain reduction and phase lag. Oculo-neck coupling or eye-head synergy was found during optokinetic stimulation in the Z and Y directions. It was characterized by bilateral activation of neck extensors and flexors during upward and downward eye movements, respectively, and by ipsilateral activation of neck muscles during horizontal eye movements. These visually-induced neck responses seemed related to eye velocity signals. Dynamic properties of neck and eye responses were significantly improved when both inputs were combined (CS). Near perfect compensatory eye movement and neck muscle responses closely related to stimulus velocity were observed over all frequencies tested, in the three directions defined. The present study indicates that eye-head coordination processes during linear motion are mainly dependent on the visual system at low frequencies (below 0.25 Hz), with close functional coupling of OKR and eye-head synergy. The otolith system basically works at higher stimulus frequencies and triggers Synergist OOR and ONR. However, both sensorimotor subsystems combine their dynamic properties to provide better eyehead coordination in an extended frequency range and, as evidenced under VS condition, visual and otolith inputs also contribute to eye and neck responses at high and low frequency, respectively. These general laws on functional coupling of the eye and head stabilizing reflexes during linear motion are valid in the three directions tested, even though the relative weight of visual and otolith inputs may vary according to motion direction and/or kinematics.     

Changes in BOLD transients with visual stimuli across 1-44 Hz

The dependency of positive BOLD (PBOLD) and post-stimulus undershoot (PSU) on the temporal frequency of visual stimulation was investigated using stimulation frequencies between 1 and 44 Hz. The PBOLD peak at 8 Hz in primary visual cortex was in line with previous neuroimaging studies. In addition to the 8 Hz peak, secondary peaks were observed for stimulation frequencies at 16 and 24 Hz. These additional local peaks were contrary to earlier fMRI studies which reported either a decrease or a plateau for frequencies above 8 Hz but in line with electrophysiological results obtained in animal local field potential (LFP) measurements and human steady-state visual evoked potential (SSVEP) recordings. Our results also indicate that the dependency of PSU amplitude on stimulus frequency deviates from that of PBOLD. Although their amplitudes were correlated within the 1-13 Hz range, they changed independently at stimulation frequencies between 13 and 44 Hz. The different dependency profiles of PBOLD and PSU to stimulation frequency points to different underlying neurovascular mechanisms responsible for the generation of these BOLD transients with regard to their relation to inhibitory and excitatory neuronal activity.     

Representation of the temporal envelope of sounds in the human brain

The cerebral representation of the temporal envelope of sounds was studied in five normal-hearing subjects using functional magnetic resonance imaging. The stimuli were white noise, sinusoidally amplitude-modulated at frequencies ranging from 4 to 256 Hz. This range includes low AM frequencies (up to 32 Hz) essential for the perception of the manner of articulation and syllabic rate, and high AM frequencies (above 64 Hz) essential for the perception of voicing and prosody. The right lower brainstem (superior olivary complex), the right inferior colliculus, the left medial geniculate body, Heschl's gyrus, the superior temporal gyrus, the superior temporal sulcus, and the inferior parietal lobule were specifically responsive to AM. Global tuning curves in these regions suggest that the human auditory system is organized as a hierarchical filter bank, each processing level responding preferentially to a given AM frequency, 256 Hz for the lower brainstem, 32-256 Hz for the inferior colliculus, 16 Hz for the medial geniculate body, 8 Hz for the primary auditory cortex, and 4-8 Hz for secondary regions. The time course of the hemodynamic responses showed sustained and transient components with reverse frequency dependent patterns: the lower the AM frequency the better the fit with a sustained response model, the higher the AM frequency the better the fit with a transient response model. Using cortical maps of best modulation frequency, we demonstrate that the spatial representation of AM frequencies varies according to the response type. Sustained responses yield maps of low frequencies organized in large clusters. Transient responses yield maps of high frequencies represented by a mosaic of small clusters. Very few voxels were tuned to intermediate frequencies (32-64 Hz). We did not find spatial gradients of AM frequencies associated with any response type. Our results suggest that two frequency ranges (up to 16 and 128 Hz and above) are represented in the cortex by different response types. However, the spatial segregation of these two ranges is not systematic. Most cortical regions were tuned to low frequencies and only a few to high frequencies. Yet, voxels that show a preference for low frequencies were also responsive to high frequencies. Overall, our study shows that the temporal envelope of sounds is processed by both distinct (hierarchically organized series of filters) and shared (high and low AM frequencies eliciting different responses at the same cortical locus) neural substrates. This layout suggests that the human auditory system is organized in a parallel fashion that allows a degree of separate routing for groups of AM frequencies conveying different information and preserves a possibility for integration of complementary features in cortical auditory regions.     

Presynaptic group II mGluR inhibition of short-term depression in the medial perforant path of the dentate gyrus in vitro

Inhibition of short-term plasticity by activation of presynaptic group II metabotropic glutamate receptors (group II mGluR) was investigated in the medial perforant path of the dentate gyrus in the hippocampus in vitro. Brief trains of stimulation (10 stimuli at 1--200 Hz) evoked short-term depression of field excitatory postsynaptic potentials (EPSPs). The steady-state level of depression, measured after 10 stimuli, was frequency dependent, increasing between 1 and 200 Hz. Activation of group II mGluR by the selective agonist LY354740 did not alter short-term depression evoked by frequencies up to 10 Hz, but did inhibit short-term depression evoked at higher frequencies in a frequency- and concentration-dependent manner. The time-averaged postsynaptic response (EPSP per unit time) was found to increase linearly with frequency up to approximately 20 Hz. At higher frequencies, the response plateaued, thereby becoming independent of frequency. Frequencies above this were differentiated only during the transient postsynaptic response that accompanies changes in firing rates. Activation of presynaptically located group II mGluR increased the frequency at which the EPSP per unit time plateaued up to 30-50 Hz.     

The autonomic innervation of the nasal blood vessels of the cat

1. A study has been made in the anaesthetized cat of the stimulation parameters required to separate the vasodilator and vasoconstrictor responses evoked in the nose by stimulating the cut peripheral end of the Vidian nerve.2. The extent of the vasodilation and vasoconstriction was found to be dependent on the stimulation frequency, but whereas vasodilation reached a maximum at 25 Hz, vasoconstriction occurred at lower frequencies and was maximum between 10 and 15 Hz.3. Atropine, in a dose much greater than that which inhibits nasal secretion, did not abolish the vasodilator responses evoked by Vidian nerve stimulation. This suggests that the Vidian nerve may convey atropine resistant fibres to the nasal vasculature.     

Carbachol effects on hippocampal neurons in vitro: dependence on the rate of rise of carbachol tissue concentration

Summary Extracellular activity from vestibular nuclei neurons and vertical eye movements were recorded in the alert cat during sinusoidal optokinetic stimulation in the vertical plane at frequencies varying from 0.0125 Hz to 0.75 Hz. Among a population of 96 vestibular units located in and around Deiters' nucleus, 73 neurons (76%) displayed a firing rate modulation which followed the input at the standard parameters of visual stimulation (0.05 Hz; 10.1 deg/s or 9.1 cm/s peak to peak velocity). Two different patterns of modulation were found. In 42 cells (57%) an increase in the firing rate was observed during motion of the visual scene in the downward direction, while 31 neurons (43%) showed the opposite behavior, with an enhanced firing rate during upward movement. The phase of the neuronal responses was close (± 45°) to the velocity peaks (+90°: downward and -90°: upward) of visual scene motion for 65 among the 73 neurons. Mean values of phase was-6.1 ± 19.5° (SD) and -3.2 ± 15.5° (SD) with respect to the +90° and -90° velocity peaks, respectively. In the frequency range 0.0125–0.75 Hz, the phase of the neuronal responses remained almost stable, with only a slight lag which reaches -22° at the 0.25 Hz visual stimulation. The firing rate modulation was found to be predominant at low frequencies (0.0125 Hz–0.25 Hz), with three distinct peaks of modulation occurring either at 0.025 Hz, 0.10 Hz or 0.25 Hz, depending on the recorded cells. Above 0.5 Hz, the cell modulation was very poorly developed or even absent. A gain attenuation was observed in all units, which was more important in cells showing a peak of modulation at 0.025 Hz as compared with the others (-20.7 dB vs -9.6 dB, respectively, in the 0.025 Hz–0.25 Hz decade). The gain of the optokinetic reflex (OKR) progressively decreased from mean values of 0.78 ± 0.15 to 0.05 ± 0.06 in the 0.025 Hz–0.5 Hz frequency range. A close correlation was observed between the OKR slow phase velocity and the modulation of the neuronal responses in the two cell populations with maximal modulations at 0.10 Hz or 0.25 Hz. No correlations were noticed in the third population characterized by a peak of modulation at 0.025 Hz. In all units, the phase of eye movement velocity and of neuronal responses were both related to the velocity of the visual surround motion. These correlations were also found when varying the amplitude of the visual stimulation at a fixed frequency. Saturation was observed in the unit responses at velocities above 68.5°/s. When considering both the gain attenuation in the frequency range and the correlation between firing rate modulation and OKR slow phase velocity, two rather different cell populations can be distinguished: one with neurons peaking at 0.025 Hz (strong gain attenuation; no correlation with OKR velocity) and one with neurons peaking at 0.10 Hz or 0.25 Hz (slight gain attenuation; correlation with OKR velocity). This study points to the influence of visual motion cues on vestibular nuclei unit activity in the low-frequency range. A velocity coding of visual — surround motion in the vertical plane is performed by vestibular neurons. Our results in the alert cat suggest that both retinal (retinal slip) and extraretinal (proprioceptive afferences from eye muscles, efference copy) inputs can be involved in this visually induced modulation of vestibular nuclei neurons.     

The auditory evoked magnetic fields to very high frequency tones

We studied the auditory evoked magnetic fields (AEFs) in response to pure tones especially at very high frequencies (from 4000 Hz to 40,000 Hz). This is the first systematic study of AEFs using tones above 5000 Hz, the upper audible range of humans, and ultrasound. We performed two experiments. In the first, AEFs were recorded in 12 subjects from both hemispheres under binaural listening conditions. Six types of auditory stimulus (pure tones of five different frequencies: 4000 Hz, 8000 Hz, 10,000 Hz, 12,000 Hz, 14,000 Hz, and a click sound as the target stimulus) were used. In the second experiment, we used 1000 Hz, 15,000 Hz, and two ultrasounds with frequencies of 20,000 Hz and 40,000 Hz. The subjects could detect all stimuli in the first experiment but not the ultrasounds in the second experiment.We analyzed N1m, the main response with approximately 100 ms in peak latency, and made the following findings. (1) N1m responses to the tones up to 12,000 Hz were clearly recorded from at least one hemisphere in all 12 subjects. N1m for 14,000 Hz was identified in at least one hemisphere in 10 subjects, and in both hemispheres in six subjects. No significant response could be identified to ultrasounds over 20,000 Hz. (2) The amplitude of the N1m to the tones above 8000 Hz was significantly smaller than that to 4000 Hz in both hemispheres. There was a tendency for the peak latency of the N1m to be longer for the tones with higher frequencies, but no significant change was found. (3) The equivalent current dipole (ECD) of the N1m was located in the auditory cortex. There was a tendency for the ECD for the tones with higher frequencies to lie in more medial and posterior areas, but no significant change was found. (4) As for the interhemispheric difference, the N1m amplitude for all frequency tones was significantly larger and the ECDs were estimated to be located more anterior and medial in the right hemisphere than the left. The priority of the right hemisphere, that is the larger amplitude, for very high frequency tones was confirmed. (5) The orientation of the ECD in the left hemisphere became significantly more vertical the higher the tones. This result was consistent with previous studies which revealed the sensitivity of the frequency difference in the left hemisphere.From these findings we suggest that tonotopy in the auditory cortex exists up to the upper limit of audible range within the small area, where the directly air-conducted ultrasounds are not reflected.