Frequency Tuning Properties Research Articles

Effect of Electrode Montage on Frequency Tuning Properties of Air-Conducted Ocular Vestibular-Evoked Myogenic Potential.

The use of a 500 Hz tone burst over other frequencies was adopted for the clinical recording of ocular vestibular-evoked myogenic potential (oVEMP) on the basis that this stimulus frequency produces larger response amplitudes (frequency tuning) than the other frequencies. However, the possibility of reflex contamination due to a spatially displaced reference electrode from the muscle of the response origin raises questions about using an infraorbital (IO) montage. Nonetheless, the belly-tendon (BT) montage, which places both the recording electrodes over the inferior oblique muscle, increases the chances of obtaining a response with greater contribution from the inferior oblique muscle. However, whether this response continues to show the frequency tuning to 500 Hz is not known. Therefore, the present study aimed to examine the frequency tuning of oVEMP using various electrode montages. Thirty-eight young adults underwent simultaneous oVEMP recording from IO, BT, chin-referenced, and sternum-referenced electrode montages in response to 250, 500, 750, 1000, 1500, 2000, 3000, and 4000 Hz tone bursts. The frequency tuning most often coincided with a 750-Hz tone burst irrespective of the montage, with the BT montage exhibiting significantly higher response rates and larger peak to peak amplitudes than other montages (p < 0.008). Further, there was a "substantial" agreement on frequency tuning between BT and IO montages. With better response rates and response amplitudes yet similar frequency tuning to the IO montage, the BT montage can be a better option for the clinical recording of oVEMP across frequencies.

Development of frequency tuning shaped by spatial cue reliability in the barn owl's auditory midbrain.

Sensory systems preferentially strengthen responses to stimuli based on their reliability at conveying accurate information. While previous reports demonstrate that the brain reweighs cues based on dynamic changes in reliability, how the brain may learn and maintain neural responses to sensory statistics expected to be stable over time is unknown. The barn owl's midbrain features a map of auditory space where neurons compute horizontal sound location from the interaural time difference (ITD). Frequency tuning of midbrain map neurons correlates with the most reliable frequencies for the neurons' preferred ITD (Cazettes et al., 2014). Removal of the facial ruff led to a specific decrease in the reliability of high frequencies from frontal space. To directly test whether permanent changes in ITD reliability drive frequency tuning, midbrain map neurons were recorded from adult owls, with the facial ruff removed during development, and juvenile owls, before facial ruff development. In both groups, frontally tuned neurons were tuned to frequencies lower than in normal adult owls, consistent with the change in ITD reliability. In addition, juvenile owls exhibited more heterogeneous frequency tuning, suggesting normal developmental processes refine tuning to match ITD reliability. These results indicate causality of long-term statistics of spatial cues in the development of midbrain frequency tuning properties, implementing probabilistic coding for sound localization.

Maturation of Heterogeneity in Afferent Synapse Ultrastructure in the Mouse Cochlea.

Auditory nerve fibers (ANFs) innervating the same inner hair cell (IHC) may have identical frequency tuning but different sound response properties. In cat and guinea pig, ANF response properties correlate with afferent synapse morphology and position on the IHC, suggesting a causal structure-function relationship. In mice, this relationship has not been fully characterized. Here we measured the emergence of synaptic morphological heterogeneities during maturation of the C57BL/6J mouse cochlea by comparing postnatal day 17 (p17, ∼3 days after hearing onset) with p34, when the mouse cochlea is mature. Using serial block face scanning electron microscopy and three-dimensional reconstruction we measured the size, shape, vesicle content, and position of 70 ribbon synapses from the mid-cochlea. Several features matured over late postnatal development. From p17 to p34, presynaptic densities (PDs) and post-synaptic densities (PSDs) became smaller on average (PDs: 0.75 to 0.33; PSDs: 0.58 to 0.31 μm2) and less round as their short axes shortened predominantly on the modiolar side, from 770 to 360 nm. Membrane-associated synaptic vesicles decreased in number from 53 to 30 per synapse from p17 to p34. Anatomical coupling, measured as PSD to ribbon distance, tightened predominantly on the pillar side. Ribbons became less spherical as long-axes lengthened only on the modiolar side of the IHC, from 372 to 541 nm. A decreasing gradient of synaptic ribbon size along the modiolar-pillar axis was detected only at p34 after aligning synapses of adjacent IHCs to a common reference frame (median volumes in nm3 × 106: modiolar 4.87; pillar 2.38). The number of ribbon-associated synaptic vesicles scaled with ribbon size (range 67 to 346 per synapse at p34), thus acquiring a modiolar-pillar gradient at p34, but overall medians were similar at p17 (120) and p34 (127), like ribbon surface area (0.36 vs. 0.34 μm2). PD and PSD morphologies were tightly correlated to each other at individual synapses, more so at p34 than p17, but not to ribbon morphology. These observations suggest that PDs and PSDs mature according to different cues than ribbons, and that ribbon size may be more influenced by cues from the IHC than the surrounding tissue.

Orientation and Contrast Tuning Properties and Temporal Flicker Fusion Characteristics of Primate Superior Colliculus Neurons.

The primate superior colliculus is traditionally studied from the perspectives of gaze control, target selection, and selective attention. However, this structure is also visually responsive, and it is the primary visual structure in several species. Thus, understanding the visual tuning properties of the primate superior colliculus is important, especially given that the superior colliculus is part of an alternative visual pathway running in parallel to the predominant geniculo-cortical pathway. In recent previous studies, we have characterized receptive field organization and spatial frequency tuning properties in the primate (rhesus macaque) superior colliculus. Here, we explored additional aspects like orientation tuning, putative center-surround interactions, and temporal frequency tuning characteristics of visually-responsive superior colliculus neurons. We found that orientation tuning exists in the primate superior colliculus, but that such tuning is relatively moderate in strength. We also used stimuli of different sizes to explore contrast sensitivity and center-surround interactions. We found that stimulus size within a visual receptive field primarily affects the slope of contrast sensitivity curves without altering maximal firing rate. Additionally, sustained firing rates, long after stimulus onset, strongly depend on stimulus size, and this is also reflected in local field potentials. This suggests the presence of inhibitory interactions within and around classical receptive fields. Finally, primate superior colliculus neurons exhibit temporal frequency tuning for frequencies lower than 30 Hz, with critical flicker fusion frequencies of <20 Hz. These results support the hypothesis that the primate superior colliculus might contribute to visual performance, likely by mediating coarse, but rapid, object detection and identification capabilities for the purpose of facilitating or inhibiting orienting responses. Such mediation may be particularly amplified in blindsight subjects who lose portions of their primary visual cortex and therefore rely on alternative visual pathways including the pathway through the superior colliculus.

Neural response differences in the rat primary auditory cortex under anesthesia with ketamine versus the mixture of medetomidine, midazolam and butorphanol

Anesthesia affects central auditory processing. However, it is unclear to what extent the choice of anesthetic agent affects neural responses to sound stimulation. A mixture of three anesthetics (medetomidine, midazolam and butorphanol; MMB) was recently developed as an alternative to ketamine owing to the latter's addictive potential, yet the effect of this combination of anesthetics on neural responses is not known. Here, we compared the spontaneous activity, tuning properties and temporal responses of primary auditory cortical neurons under these two anesthetic conditions, using electrophysiological and flavoprotein autofluorescence imaging methods. Frequency tuning properties were not significantly different between ketamine and MMB anesthesia. However, neural activity under MMB showed decreases in the spontaneous and tone-evoked firing rates in a layer-dependent manner. Moreover, the temporal response patterns were also different between the anesthetics in a layer-dependent manner, which may reflect differences in the anesthetic mechanisms. These results demonstrated how response properties in the primary auditory cortex are affected by the choice of anesthesia.

Effects of Electrical Stimulation in the Inferior Colliculus on Frequency Discrimination by Rhesus Monkeys and Implications for the Auditory Midbrain Implant.

Understanding the relationship between the auditory selectivity of neurons and their contribution to perception is critical to the design of effective auditory brain prosthetics. These prosthetics seek to mimic natural activity patterns to achieve desired perceptual outcomes. We measured the contribution of inferior colliculus (IC) sites to perception using combined recording and electrical stimulation. Monkeys performed a frequency-based discrimination task, reporting whether a probe sound was higher or lower in frequency than a reference sound. Stimulation pulses were paired with the probe sound on 50% of trials (0.5-80 μA, 100-300 Hz, n = 172 IC locations in 3 rhesus monkeys). Electrical stimulation tended to bias the animals' judgments in a fashion that was coarsely but significantly correlated with the best frequency of the stimulation site compared with the reference frequency used in the task. Although there was considerable variability in the effects of stimulation (including impairments in performance and shifts in performance away from the direction predicted based on the site's response properties), the results indicate that stimulation of the IC can evoke percepts correlated with the frequency-tuning properties of the IC. Consistent with the implications of recent human studies, the main avenue for improvement for the auditory midbrain implant suggested by our findings is to increase the number and spatial extent of electrodes, to increase the size of the region that can be electrically activated, and to provide a greater range of evoked percepts. Patients with hearing loss stemming from causes that interrupt the auditory pathway after the cochlea need a brain prosthetic to restore hearing. Recently, prosthetic stimulation in the human inferior colliculus (IC) was evaluated in a clinical trial. Thus far, speech understanding was limited for the subjects and this limitation is thought to be partly due to challenges in harnessing the sound frequency representation in the IC. Here, we tested the effects of IC stimulation in monkeys trained to report the sound frequencies they heard. Our results indicate that the IC can be used to introduce a range of frequency percepts and suggest that placement of a greater number of electrode contacts may improve the effectiveness of such implants.

Visual Receptive Field Properties of Neurons in the Mouse Lateral Geniculate Nucleus.

The lateral geniculate nucleus (LGN) is increasingly regarded as a “smart-gating” operator for processing visual information. Therefore, characterizing the response properties of LGN neurons will enable us to better understand how neurons encode and transfer visual signals. Efforts have been devoted to study its anatomical and functional features, and recent advances have highlighted the existence in rodents of complex features such as direction/orientation selectivity. However, unlike well-researched higher-order mammals such as primates, the full array of response characteristics vis-à-vis its morphological features have remained relatively unexplored in the mouse LGN. To address the issue, we recorded from mouse LGN neurons using multisite-electrode-arrays (MEAs) and analysed their discharge patterns in relation to their location under a series of visual stimulation paradigms. Several response properties paralleled results from earlier studies in the field and these include centre-surround organization, size of receptive field, spontaneous firing rate and linearity of spatial summation. However, our results also revealed “high-pass” and “low-pass” features in the temporal frequency tuning of some cells, and greater average contrast gain than reported by earlier studies. In addition, a small proportion of cells had direction/orientation selectivity. Both “high-pass” and “low-pass” cells, as well as direction and orientation selective cells, were found only in small numbers, supporting the notion that these properties emerge in the cortex. ON- and OFF-cells showed distinct contrast sensitivity and temporal frequency tuning properties, suggesting parallel projections from the retina. Incorporating a novel histological technique, we created a 3-D LGN volume model explicitly capturing the morphological features of mouse LGN and localising individual cells into anterior/middle/posterior LGN. Based on this categorization, we show that the ON/OFF, DS/OS and linear response properties are not regionally restricted. Our study confirms earlier findings of spatial pattern selectivity in the LGN, and builds on it to demonstrate that relatively elaborate features are computed early in the visual pathway.

Cooling of the auditory cortex modifies neuronal activity in the inferior colliculus in rats

There are powerful pathways descending from the auditory cortex (AC) to the inferior colliculus (IC), yet their function is not fully understood. The aim of this study is to examine the effects of a reversible cortical inactivation, achieved by cooling of the AC, on the responses of neurons in the rat IC. Extracellular single-unit or multi-unit activity was recorded in the IC of anaesthetized rats with a 16-channel multielectrode probe introduced along the IC dorso-ventral axis through the dorsal cortex (DCIC) to the central nucleus of the IC (CIC). Cooling of the AC produced an increase in spontaneous activity and magnitude of the sound-evoked response in 47% of the IC neurons. Maximal changes in the neuronal activity were observed in the DCIC and the central part of the CIC. The final segments of the sustained responses to 60 ms stimuli and the off responses were more affected than the onset segments. Inactivation of the AC resulted in a suppression of the post-excitatory inhibition and neuronal adaptation, which was reflected in a pronounced enhancement of synchronized responses to a series of fast repeated clicks. The response parameters recovered, at least partly, to the pre-cooling levels 1 h after the cooling cessation. The frequency tuning properties of the IC neurons did not show any significant changes during the cooling period. The results demonstrate that AC cooling inactivates excitatory corticofugal pathways and results in a less activated intrinsic inhibitory network in the IC.

Changes of spatial and temporal frequency tuning properties of neurons in the middle temporal area of aged rhesus monkeys

Aged humans exhibit severe deficits in visual motion perception and contrast sensitivity under various levels of spatial and temporal modulation. Previous studies indicated that many of these deficits are probably mediated by the neural degradation of the central visual system. To clarify the neuronal response mechanisms underlying the visual degradation during aging, we examined the spatial and temporal frequency tuning properties of neurons from anesthetised and paralysed aged monkeys at the middle temporal area (area MT), which is downstream of the primary visual cortex in the visual processing pathway and thought to be critical for motion perception. We found that the preferred spatial and temporal frequencies, spatial resolution and high temporal frequency cutoff of area MT neurons were reduced in aged monkeys, and were accompanied by the broadened tuning width of spatial frequency, elevated spontaneous activity, and decreased signal-to-noise ratio. These results showed that, for neurons in area MT, aging significantly changed both the spatial and temporal frequency response tuning properties. Such evidence provides new insight into the changes occurring at the electrophysiological level that may be related to the aging-related visual deficits, especially in processing spatial and temporal information.

Spatial pattern of intra-laminar connectivity in supragranular mouse auditory cortex

Neuronal responses and topographic organization of feature selectivity in the cerebral cortex are shaped by ascending inputs and by intracortical connectivity. The mammalian primary auditory cortex has a tonotopic arrangement at large spatial scales (greater than 300 microns). This large-scale architecture breaks down in supragranular layers at smaller scales (around 300 microns), where nearby frequency and sound level tuning properties can be quite heterogeneous. Since layer 4 has a more homogeneous architecture, the heterogeneity in supragranular layers might be caused by heterogeneous ascending input or via heterogeneous intralaminar connections. Here we measure the functional 2-dimensional spatial connectivity pattern of the supragranular auditory cortex on micro-column scales. In general connection probability decreases with radial distance from each neuron, but the decrease is steeper in the isofrequency axis leading to an anisotropic distribution of connection probability with respect to the tonotopic axis. In addition to this radial decrease in connection probability we find a patchy organization of inhibitory and excitatory synaptic inputs that is also anisotropic with respect to the tonotopic axis. These periodicities are at spatial scales of ~100 and ~300 μm. While these spatial periodicities show anisotropy in auditory cortex, they are isotropic in visual cortex, indicating region specific differences in intralaminar connections. Together our results show that layer 2/3 neurons in auditory cortex show specific spatial intralaminar connectivity despite the overtly heterogeneous tuning properties.

Characterizing the frequency tuning properties of air-conduction ocular vestibular evoked myogenic potentials in healthy individuals

Objective: Inconsistencies regarding frequency tuning of ocular vestibular evoked myogenic potentials (oVEMP) prompted the present study to aim at characterizing frequency tuning of oVEMP in healthy individuals. Design: Normative study. Study sample: The study was conducted to obtain oVEMP responses from 54 healthy individuals in age range of 18–30 years. The responses were acquired for tone-bursts at octave and mid-octave frequencies from 250 to 2000 Hz from the inferior oblique muscle using contralateral electrode placement. The frequencies were compared for amplitude and threshold. Results: oVEMPs were present in 100% of individuals at or below the frequency of 1000 Hz. The responses had maximum amplitude and lowest thresholds at 500 Hz. There were at least two replicable peak-complexes namely n1-p1 and p1-n2. Both these complexes revealed tuning at 500 Hz. Comparison between the two peak-complexes revealed higher amplitudes and lower thresholds for p1-n2 complex. Conclusions: oVEMPs are tuned to 500 Hz for both peak-complexes, with p1-n2 being more robust. Future studies using the threshold of oVEMP may be better suited to use p1-n2 complex for this purpose, provided vestibular origin of the second complex is proved. Additionally, careful use of tuning property is recommended when evaluating pathological conditions.

Design of a tunable terahertz narrowband metamaterial absorber based on an electrostatically actuated MEMS cantilever and split ring resonator array

A dynamically tunable terahertz (THz) narrowband metamaterial absorber is presented. The absorber is based on an electrostatically actuated micro-electro-mechanical systems (MEMS) cantilever and split ring resonator (SRR) array. An equivalent LC circuit model for a transverse electric (TE) polarization wave is introduced to analyze the mechanism of frequency tuning. A finite element method is applied to simulate the mechanical characteristics of the cantilever, and a finite integration technique is used to study the frequency tuning properties of the absorber. The results show that, for a TE polarization wave, there is only one absorption peak in the frequency range from 0.6 to 1.6 THz. The absorption peak frequency can be continuously tuned from 1.32 to 1.28 THz, and then abruptly to 1.12 THz. The maximum tunable frequency is 0.20 THz, which is about 15% of the initial resonance frequency. For a transverse magnetic (TM) polarization wave, there are two tunable absorption peaks in this frequency range. Moreover, for a TE wave, some geometric dimensions affecting the initial resonance frequency are investigated.

Frequency Tuning of the Cervical Vestibular-Evoked Myogenic Potential (cVEMP) Recorded from Multiple Sites along the Sternocleidomastoid Muscle in Normal Human Subjects

Frequency tuning of tone burst-evoked myogenic potentials recorded from the sternocleidomastoid muscle (cervical VEMP or cVEMP) is used clinically to assess vestibular function. Understanding the characteristics of cVEMP is important for improving the specificity of cVEMP testing in diagnosing vestibular deficits. In the present study, we analyzed the frequency tuning properties of the cVEMPs by constructing detailed tuning curves and examining their morphology and dependence on SCM tonic level, sound intensity, and recording site along the SCM. Here we report two main findings. First, by employing nine tone frequencies between 125 and 4,000 Hz, some tuning curves exhibited two distinct peaks, which cannot be modeled by a single mass spring system as previously suggested. Instead, the observed tuning is better modeled as linear summation of two mass spring systems, with resonance frequencies at ~300 and ~1,000 Hz. Peak frequency of cVEMP tuning curves was not affected by SCM tonic level, sound intensity, and location of recording site on the SCM. However, sharpness of cVEMP tuning was increased at lower sound intensities. Second, polarity of cVEMP responses recorded from the lower quarter of the SCM was reversed as compared to that at the two upper sites. While more studies are needed, these results suggest that cVEMP tuning is mediated through multiple generators with different resonance frequencies. Future studies are needed to explore implications of these results on development of selective VEMP tests and determine the nature of polarity inversion at the lower quarter of SCM.

Frequency tuning of the contralateral medial olivocochlear reflex in humans

Activation of the medial olivocochlear (MOC) efferents attenuates cochlear gain and reduces the amplitudes of mechanical, electrical, and neural cochlear outputs. The functional roles of the MOC efferents are not fully understood, especially in humans, despite postulations that they are involved in protection against acoustic trauma, facilitation of transient-sound perception, etc. Delineating the frequency tuning properties of the MOC efferents would provide critical evidence to support or refute these postulated functional roles. By utilizing spontaneous otoacoustic emissions (SOAEs), a cochlear measure sensitive to MOC modulation, we systematically demonstrate in humans that the contralateral MOC reflex is tuned to a fixed frequency band between 500 and 1,000 Hz independent of SOAE frequency. Our results question the role of the MOC reflex in protection against acoustic trauma or facilitation of transient-sound perception.

The Y Cell Visual Pathway Implements a Demodulating Nonlinearity

Neural encoding of sensory signals involves both linear and nonlinear processes. Determining which nonlinear operations are implemented by neural systems is crucial to understanding sensory processing. Here, we ask if demodulation, the process used to decode AM radio signals, describes how Y cells in the cat LGN nonlinearly encode the visual scene. In response to visual AM signals acrossa wide range of carrier frequencies, Y cells were found to transmit a demodulated signal, with the firing rate of single-units fluctuating at the envelope frequency but not the carrier frequency. A comparison of temporal frequency tuning properties between LGN Y cells and neurons in two primary cortical areas suggests that Y cells initiate a distinct pathway that carries a demodulated representation of the visual scene to cortex. The nonlinear signal processing carried out by the Y cell pathway simplifies the neural representation of complex visual features and allows high spatiotemporal frequencies to drive cortical responses.

The Influence of Contrasts on Directional and Spatial Frequency Tuning in Visual Cortex Areas 17/18 of the Cat

PurposeThe purpose of this study was to investigate the effects of contrast display exposure on neuronal directional and spatial frequency tuning. Neuronal responses were recorded from ninety-four neurons in cortical areas 17 and 18 in two adult cats.MethodsA multi-channel microelectrode was implanted in cortical areas 17 and 18 of two paralyzed and anaesthetized cats. Various drifting sinusoidal grating contrast displays were presented to one of the cats' eyes in the visual field. Contour plots based on the neuronal responses to the drifting sinusoidal grating displays using various contrasts (i.e., 0.4, 0.7, and 1.0) and velocities (i.e., 4.6, 13.9, 23.1, 32.3, 41.5, 50.8, and 60.0 deg/sec) were plotted as a function of the spatial frequency and the direction associated with each velocity and contrast used.ResultsFive parameters were extracted from these contour plots: 1) optimum response, 2) preferred direction, 3) optimum spatial frequency, 4) directional tuning width, and 5) spatial frequency bandwidth. To determine the optimal velocity, each parameter was plotted against each of the specific display contrasts used, and a 'best fit' line was established. Response amplitudes were dependent on the type of contrast utilized; however, the spatial frequency and directional tuning properties were stable for the cortical neurons assessed.ConclusionsThe results of the presentation of different contrasts on neuronal directional and spatial frequency tuning are consistent with behavioral results when medium and high contrast displays are used.

GABAergic Inhibition Sharpens the Frequency Tuning and Enhances Phase Locking in Chicken Nucleus Magnocellularis Neurons

GABAergic modulation of activity in avian cochlear nucleus neurons has been studied extensively in vitro. However, how this modulation actually influences processing in vivo is not known. We investigated responses of chicken nucleus magnocellularis (NM) neurons to sound while pharmacologically manipulating the inhibitory input from the superior olivary nucleus (SON). SON receives excitatory inputs from nucleus angularis (NA) and nucleus laminaris (NL), and provides GABAergic inputs to NM, NA, NL, and putatively to the contralateral SON. Results from single-unit extracellular recordings from 2 to 4 weeks posthatch chickens show that firing rates of auditory nerve fibers increased monotonically with sound intensity, while that of NM neurons saturated or even decreased at moderate or loud sound levels. Blocking GABAergic input with local application of TTX into the SON induced an increase in firing rate of ipsilateral NM, while that of the contralateral NM decreased at high sound levels. Moreover, local application of bicuculline to NM also increased the firing rate of NM neurons at high sound levels, reduced phase locking, and broadened the frequency-tuning properties of NM neurons. Following application of DNQX, clear evidence of inhibition was observed. Furthermore, the inhibition was tuned to a broader frequency range than the excitatory response areas. We conclude that GABAergic inhibition from SON has at least three physiological influences on the activity of NM neurons: it regulates the firing activity of NM units in a sound-level-dependent manner; it improves phase selectivity; and it sharpens frequency tuning of NM neuronal responses.

Responses of neurons in the rat's dorsal cortex of the inferior colliculus to monaural tone bursts

Responses to contralaterally presented tone bursts were recorded from single auditory neurons in the rat's dorsal cortex of the inferior colliculus (ICd). Most of these neurons either had low level of firing or generated no action potentials in the absence of sound stimulation. In response to tone bursts, about half of the ICd neurons fired at the onset while about 40% of the neurons fired over the entire duration of the sounds. The remaining ICd neurons fired transiently at the offset or both the onset and the offset of the sounds. In comparison with neurons in the central nucleus of the inferior colliculus, neurons in the ICd had much longer first spike latencies and much larger magnitudes of jitter in the first spike latency. Many neurons in the ICd displayed complex frequency tuning properties. No strong correlation was revealed between the characteristic frequency of a neuron and its location along an axis oriented from a rostrodorsolateral to a caudoventromedial part of the ICd. There are neurons in the ICd showing stimulus-specific adaptation. For these neurons, presentations of a tone burst elicited stronger responses when these presentations were embedded in a train of tone bursts with various different frequencies than clustered in a block. Neurons with stimulus-specific adaptation displayed phasic firing at the onset of a tone burst. Our results suggest that the ICd is important for detecting novel sounds in the acoustic environment.

Temporal Changes of Direction and Spatial Frequency Tuning in Visual Cortex Areas 17 and 18

Spatial frequency and direction tuning to drifting sinusoidal gratings are intrinsic properties of neurons in visual cortex neurons in areas 17 and 18. To investigate the stability of these tuning properties during visual stimulation in anesthetized cats, the temporal dynamics of spatial frequency and direction tuning were analyzed in every 0.1 sec. The responses of cortical neurons (n=109) as a function of spatial frequency as well as direction at a particular velocity for 1 second were measured and plotted as a contour plot. Five parameters from this plot were extracted: optimum response, preferred direction (direction that showed the optimum response), optimum spatial frequency (spatial frequency that showed the optimum response), direction tuning width (the difference between the highest and lowest directions to which the cell was at least half as responsive as it was to its optimum direction) and spatial frequency bandwidth (the difference between the highest and lowest frequencies to which the cell was at least half as responsive as it was to its optimum frequency). Then, this contour plot was further analyzed in every 0.1 sec to investigate whether these five parameters were changed or not during the course of stimulation. These parameters were plotted along the time (0.1 sec step) and a line of fit was found. Both spatial frequency and direction tuning properties were not changed in most of the cells. This suggests that both direction and spatial frequency tuning properties are stable during drifting sinusoidal gratings’ stimulation.

Frequency tuning properties of ocular vestibular evoked myogenic potentials

Loud air-conducted sound or bone-conducted vibration produces vestibular-dependent electromyographic responses both in the cervical muscles (cervical vestibular evoked myogenic potentials) and in the extraocular muscles (ocular vestibular evoked myogenic potentials; oVEMPs). Although previous frequency tuning measurements of cervical vestibular evoked myogenic potentials have provided important information for a clinical application, those of oVEMPs have rarely been studied. We explored the frequency tuning properties of oVEMPs in 12 healthy participants. Our results indicate that the best frequencies of the oVEMPs to air-conducted sound and bone-conducted vibration are 500 and 250 Hz, respectively. The difference in the best frequencies between the two stimuli may originate from the difference in the end organs (saccule or utricle), preferentially activated by each stimulus.