Ipsilateral Stimuli Research Articles

Bimodal extinction without cross-modal extinction.

Three patients with unilateral neurological injury were clinically examined. All showed consistent unilateral extinction in the tactile and visual modalities on simultaneous intramodal stimulation. There was virtually no evidence for cross-modal extinction, however, so that contralateral stimulation of one modality would have extinguished perception of ipsilateral stimuli in the other modality. It is concluded that the attentional system controlling the encoding of tactile and visual stimuli is not unified across the two sensory domains.

Otoacoustic Emissions.

Otoacoustic emissions are low-intensity sounds that are produced in the cochlea and transmitted through the middle ear apparatus to the ear canal. They can be detected and extracted from the background noise in the ear canal through the use of a sensitive microphone and selective filtering or averaging techniques. The technical aspects of emission recording are very similar to those associated with the detection and capture of auditory evoked potentials. Emissions provide an acoustic link to a physiological window through which we can view the auditory periphery using frequency-specific stimuli that are presented at low and moderate intensities. The window provides an opportunity to examine cochlear activity that occurs prior to stimulation of the nervous system.Tonal emissions occur spontaneously in approximately 40% of people who have normal thresholds for pure-tone stimuli. SOAE and other types of emissions may be influenced by both ipsilateral and contralateral stimuli. One form of interaction results in suppression of the emission, and the tuning patterns associated with suppression of emissions by ipsilateral stimuli have characteristics that are similar to tuning patterns associated with single cochlear hair cells and individual neurons of the auditory nerve. These findings and other lines of evidence support the conclusion that an emission having tonal characteristics is produced from a very restricted region of the cochlear partition.Emissions may be evoked by brief click or tonal stimuli, and by continuous tonal stimuli, in virtually all individuals who have normal pure-tone thresholds and uncompromised middle ear systems. The EOAE are compromised by conditions that compromise the function of the cochlea, and they hold promise as tools that might be employed in screening for hearing loss. Preliminary findings suggest that screening employing TEOAE produces a yield that is similar to that produced by screening programs based on auditory brainstem responses. Emissions may offer advantages over current screening methods because of the ease with which they can be recorded and their apparent independence from neurological influence.Many questions regarding the origin and nature of emissions remain unanswered, but they appear to offer great sensitivity to the status of the auditory periphery. DPOAE provide an opportunity to scan the cochlear partition from base to apex with frequency-specific stimuli, and give the examiner a detailed view of the status of the end organ. The study of DPOAE holds great promise in refinement of site of lesion identification. It is exciting to witness the development of a tool to help clinical examiners probe the function of the previously inaccessible cochlea.

Interactions in human quadriceps-triceps surae motoneuron pathways

In an effort to more fully investigate spinal reflex pathways in humans, we measured the isometric force-time curve of the patellar (PTR) and Achilles (ATR) tendon-tap reflex in 12 college age subjects. We also conditioned the tendon jerk with a contralateral or ipsilateral tendon-tap stimulus, to ascertain the effects of segmental inputs on crossed-spinal reflex activity. The conditioning stimulus preceded the test reflex by 25, 40, 55, 70, 85, 100, 115, 130 or 145 ms. The results demonstrate that a tap to the contralateral patellar tendon produced long-latency excitation of quadriceps motoneurons, but a tap to the contralateral Achilles tendon produced short-latency facilitation and long-latency inhibition of the triceps surae motoneurons. Also, a conditioning tap to the contra- or ipsilateral patellar tendon produced a brief short-latency facilitation that was followed by a distinct, long-latency inhibition of triceps surae motoneurons. These results demonstrate that motoneuron excitability changes can be produced as a result of ispi- and contralateral segmental inputs. Moreover, these excitability changes may be long-lasting and only appear after a relatively long-latency. Several neurophysiological mechanisms are proposed to contribute to these changes.

Auditory Interneurones in the Metathoracic Ganglion of the Grasshopper Chorthippus Biguttulus: I. Morphological and Physiological Characterization

ABSTRACT Auditory interneurones originating in the metathoracic ganglion of females of the grasshopper Chorthippus biguttulus can be classified as local (SN), bisegmental (BSN), T-shaped (TN) and ascending neurones (AN). A comparison of branching patterns and physiological properties indicates that auditory interneurones of C. biguttulus are homologous with those described for the locust. Eighteen types of auditory neurones are morphologically characterized on the basis of Lucifer Yellow staining. All of them branch bilaterally in the metathoracic ganglion. Smooth dendrites, from which postsynaptic potentials (PSPs) can be recorded, predominate on the side ipsilateral to the soma. If ‘beaded’ branches exist, they predominate contralaterally. The ascending axon runs contralaterally to the soma, except in T-fibres. Auditory receptors respond tonically. The dynamic range of their intensityresponse curve covers 20–25 dB. Local, bisegmental and T-shaped neurones are most sensitive to stimulation ipsilateral to the soma. The responses of SN1 and TNI to white-noise stimuli are similar to those of receptors, while phasic-tonic responses are found in SN4, SN5, SN7 and BSN1. The bisegmental neurones receive side-dependent inhibition that corresponds to a 20-30dB attenuation. One local element (SN6) is predominantly inhibited by acoustic stimuli. Ascending neurones are more sensitive to contralateral stimulation (i.e. on their axon side). Only one of them (AN6) responds tonically to white-noise stimuli at all intensities; others exhibit a tonic discharge only at low or at high intensities. One neurone (AN12) responds with a phasic burst over a wide intensity range. The most directional neurones (AN1, AN2) are excited by contralateral stimuli and (predominantly) inhibited by ipsilateral stimuli. Three ascending neurones (AN13–AN15) are spontaneously active and are inhibited by acoustic stimuli. All auditory interneurones, except SN5, are more sensitive to pure tones below 10 kHz than to ultrasound.

Low-frequency neurons in the lateral superior olive exhibit phase-sensitive binaural inhibition

1. Responses of low characteristic frequency (CF) neurons in the lateral limb of the lateral superior olive (LSO) of chinchilla and rat to binaural stimuli at various interaural phase and intensity differences were examined and compared to responses from previous studies of high CF neurons. 2. Ninety-six LSO neurons from chinchillas and 10 LSO neurons from rats with CFs less than 1,200 Hz were characterized. The majority of these neurons displayed phase-locked tone-evoked temporal discharge patterns to ipsilateral CF stimuli. 3. Similar to high-CF LSO neurons, low-CF LSO neurons were excited by ipsilateral stimuli and inhibited by contralateral stimuli, with discharge rate sensitive to interaural intensity differences (IID). Discharge rate increased as ipsilateral intensity was increased and decreased as contralateral stimulus intensity was increased. 4. Binaural inhibition, inhibition of ipsilaterally evoked activity by contralateral stimuli, was dependent on interaural phase differences (IPD) in the majority of low-CF LSO neurons. Responses of phase-sensitive neurons to binaural stimuli often varied with 90 or 180 degrees changes in IPD from total inhibition to a facilitated response when compared to responses to control ipsilateral stimuli alone. 5. In summary, like high-CF LSO neurons, LSO neurons with low CFs (less than 1,200 Hz) were ipsilaterally excited and contralaterally inhibited (EI) and were sensitive to IID. Unlike most high-CF EI LSO neurons, which are not responsive when the azimuth of the stimulus is directly in front of or directly behind the animal, many low-CF LSO neurons are responsive to these stimuli.(ABSTRACT TRUNCATED AT 400 WORDS)

Idiopathic trigeminal pain associated with gustatory stimuli

We present a unique case of a patient with facial pain evoked by gustatory stimuli. Pain was typically evoked by application of sucrose to the ipsilateral anterior 2 3 of the tongue, but not to the contralateral aspect. Pain was referred to the maxillary tuberosity area and, when stronger, to the infraorbital and supraorbital regions. Sucrose was most effective in eliciting pain, whilst saline, citric acid and water had a minimal effect. Spatial or temporal summation of gustatory stimuli was associated with stronger pain of longer duration and shorter latency. Some of the pain characteristics were similar to those of idiopathic trigeminal neuralgia. Thus, pain was elicited by innocuous ipsilateral stimuli, referred out of the stimulus zone, persisted beyond the period of stimulation and could be controlled with carbamazepine. We proposed a central neural mechanism for pain induction with convergence between gustatory stimuli afferents and pain pathways in the trigeminal system.

Some aspects of time, stimulus complexity, and gender in 40‐Hz EEG responses

The present study investigated 40‐Hz EEG responses of 17 listeners who received ipsilateral and contralateral story and click stimuli. An initial comparison between loudness adaptation and 40‐Hz activity failed to show any change in central activity corresponding to change in loudness judgments. For the complete sample of listeners, a significant interaction was found between stimulus complexity, ear, and 40‐Hz response quadrant. Subsequent investigation of gender differences across the temporal region suggests an extension of conclusions offered recently by Kimura. Implications will be discussed.

Differences between ipsilaterally and contralaterally evoked potentials in the visual wulst of the zebra finch

The telencephalic target of the thalamofugal visual pathway in birds, the visual wulst, is part of the hyperstriatum accessorium/dorsale in the bird's brain. In this study, we tried to determine the exact location of the visually responsive area in the zebra finch by recording visually evoked potentials (VEPs) from different sites throughout the hyperstriatum and calculating current source densities (CSDs). In addition, we examined the influence of ipsilateral and contralateral stimuli on stimulus processing within this area, and tried to get insight into the neuronal machinery of the thalamofugal pathway by application of drugs such as tetrodotoxin (TTX) and picrotoxin. About two-thirds of the hyperstriatum is responsive to contralateral stimuli but only a small portion responds to ipsilateral stimuli. Contralateral visual information arrives in the hyperstriatum dorsale (HD) and is processed further to the hyperstriatum accessorium (HA). The small influence of ipsilaterally evoked potentials is not due to inhibition by the activity of the contralateral eye, as could be demonstrated previously for the ectostriatum. Instead, our results show that ipsilaterally evoked potentials are inhibited at least in part by a projection from the contralateral visual wulst.

Sensorimotor cortical lesion effects and treatment with nimodipine

Rats with unilateral ablations of the sensorimotor cortex and others with control operations were tested for their ability to touch and remove adhesive tape applied to both forelimbs. Half of each group was administered a calcium channel antagonist (nimodipine) for two weeks following the lesions and the other half received vehicle. The rats with lesions showed a bias to remove the ipsilateral stimulus first and exhibited contralateral deficits relative to control animals. Nimodipine was shown to reduce the contralateral stimulus removal time when the animals began testing two weeks after surgery, but not when testing began 1 day after surgery and overlapped the period of drug administration. Lesion effects also appeared on tests for neurologic impairment and activity, but nimodipine did not reduce these deficits. These findings indicate that nimodipine has the potential to reduce some deficits after sensorimotor cortical lesions, but that the effects of this drug may be task specific.

Transcutaneous electrical stimulation applied to the infratrochlear nerve induces a homatropine-resistant miosis in humans

1. Both high- and low-intensity transcutaneous electrical stimuli were applied to the emergence of the infratrochlear nerve in 18 healthy subjects. The effect on the size of the homolateral pupil was investigated. The width of the pupil was also measured when high-intensity transcutaneous electrical stimulation was applied to the contralateral side. 2. The high-intensity pulse resulted in constriction of the pupil when the stimulation was homolateral. The miosis was slow in onset (120 s latency) and long-lasting (80 s). No pupillary changes were detected after either ipsilateral low-intensity or contralateral high-intensity stimuli. 3. In 11 healthy subjects, the pupillary response to transcutaneous electrical stimulation was evaluated during iris parasympathetic blockade induced by homatropine eyedrops. The disappearance of the light reflex due to homatropine was considered an index of the parasympathetic blockade. Afterwards, a high-intensity pulse was transcutaneously delivered to the emergence of the infratrochlear nerve and the ipsilateral pupil size was measured. 4. A reduction in the pupillary size followed the electrical stimulation, still under the effect of homatropine which abolished the light reflex. The time course of this pupillary constriction was similar to that seen without the influence of homatropine. 5. The findings suggest that homolateral miosis, observed after unilateral high-intensity stimulation of the infratrochlear nerve, does not stem from cholinergic activation. It has been suggested that miosis induced by transcutaneous electrical stimulation may be due to an antidromic activation of the iris sensory fibres.

Flash evoked potentials in the ectostriatum of the zebra finch: a current source-density analysis.

Recent research has demonstrated that ipsilaterally visually evoked potentials (VEPs) can be measured within the ectostriatum, the telencephalic target area of the tectofugal visual pathway in birds. In this paper we systematically measured contra- and ipsilateral VEPs within the ectostriatal complex to obtain more detailed information on the processing of contra- and ipsilateral stimuli. The similarity of neighbouring VEPs at equal depth and a comparison of a one dimensional and a three dimensional analysis of current source-densities (CSDs) for identical coordinates suggested that a one dimensional current source-density analysis might be applicable. The one dimensional current source-density analysis demonstrated largely corresponding patterns in the sink-source sequences of the current source-density depth profiles for the contra- and ipsilateral stimulus responses. The occurrence of a large sink in the centre of the ectostriatal core, together with the results of multiunit recordings, shows that the ectostriatal core is the location of the generators for both the contra- and the ipsilaterally evoked responses. The occurrence of macroscopic sinks and sources and the fact that VEPs can be recorded from the ectostriatum shows that there is a higher degree of order in the ectostriatum than has been previously demonstrated by anatomical methods. The time coincidence between the maximum spike rate of multiunit responses, the negative peak of the evoked potential, and the large central sink demonstrates that the influence of ipsi- as well as of contralateral stimuli is predominantly excitatory.

Topographical analysis of subcortical vertex-like activities evoked by ipsi- and contralateral multimodal sensory stimulation in man.

A topographical analysis of the mesencephalic, thalamic and forebrain vertex-like activities evoked by ipsi- and contralateral somatic (SVA), visual (VVA) and auditory stimuli (AVA) was made in patients with electrodes implanted for diagnoses and treatment. Typical SVA, VVA and AVA recorded from a nonspecific polysensory system (NSS) were mainly bilateral and with similar latencies. Typical AVA to only contralateral stimuli were frequent at the ventrolateral thalamus and striatum level. In contrast, bilateral VA with different latencies and VA evoked only by ipsilateral stimuli were rare and mainly localized at the edge of the NSS. Within the NSS, typical VA to ipsi- and contralateral stimuli showed different cerebral distribution patterns according to the sensory modality stimulated, i.e. SVA showed amplitudes in response to contralateral stimuli smaller than to ipsilateral stimuli at the mesencephalic level, larger amplitudes in response to contralateral than to ipsilateral stimuli at the thalamic level and had equal amplitudes in response to contralateral and ipsilateral stimuli in the forebrain regions. VVA showed amplitudes in response to contralateral stimuli equal to those in response to ipsilateral stimuli at the mesencephalic, thalamic and forebrain levels. AVA showed amplitudes in response to contralateral stimuli equal to those in response to ipsilateral stimuli at the mesencephalic level, had amplitudes of contralateral responses larger than those of ipsilateral responses at the thalamic level and showed different amplitude combinations in the forebrain regions.

Effects of contralateral sound on auditory-nerve responses. II. Dependence on stimulus variables

The suppression by moderate-level contralateral sound of auditory-nerve-fiber responses to ipsilateral stimuli at the characteristic frequency (CF) was studied in barbiturate-anaesthetized cats. The dependence of suppression strength on ipsilateral and contralateral stimulus variables, including level, frequency, bandwidth, and timing relationships, was investigated. The principal findings were: (1) Contralateral-sound suppression is greatest when the ipsilateral stimulus level is within the dynamic range of the unit. (2) When the contralateral stimuli are tones, suppression is greatest when the contralateral tone frequency is at or near CF. (3) Units with CFs above 3–4 kHz are only weakly suppressed by contralateral CF tones but more strongly suppressed by contralateral broad-band noise. (4) Continuous contralateral stimuli are significantly more effective suppressors than are gated stimuli. The characteristics of contralateral-sound suppression are compared with the physiology and anatomy of the uncrossed medial olivocochlear efferents, the subset of efferents which are the primary mediators of the effect.

Interaural interaction in the human auditory cortex.

We studied the effect of binaural, contralateral and ipsilateral stimulation on middle- and long-latency auditory-evoked magnetic fields using trains of 40-Hz clicks. The stimuli evoked both a transient response (N100m) and a 40-Hz response, which presumably reflects coalescence of middle-latency responses. Binaural stimuli elicited significantly larger 40-Hz responses and sustained fields than contralateral stimuli. N100m amplitudes did not differ between binaural and contralateral stimulation; the dipole moments were even smaller to binaural than contralateral stimuli. Responses to the ipsilateral stimuli were always the smallest.

Response properties of cochlear efferent neurons: monaural vs. binaural stimulation and the effects of noise

1. Discharge properties of olivocochlear efferent neurons were measured in anesthetized cats. Previous studies of these neurons concentrated on monaural stimulation with tones and found sound-evoked discharge rates rarely exceeded 60 spikes/s (16, 20). In the present study, rates as high as 140 spikes/s were achieved by binaural stimulation and/or the addition of noise. Based on studies on the known effects of electrically stimulating the efferents such high rates of sound-evoked efferent activity probably have significant feedback effects on the auditory periphery. 2. Spontaneous discharge rate (SR) was weakly correlated with threshold among efferent neurons: those with SRs greater than 1 spikes/s were generally more sensitive than spontaneously inactive fibers. The discharge rate measured in the absence of acoustic stimulation was shown to be dependent on stimulation history: some units with zero SR became spontaneously active after several minutes of continuous noise stimulation. 3. For stimulation with monaural tones, efferent excitability varied with characteristic frequency (CF): units with CF less than 10 kHz tended to have lower thresholds, higher discharge rates, and shorter latencies than higher CF units. These differences could be minimized by the addition of broadband noise (see below). 4. When tones were presented to one ear at a time, most efferent units appeared monaural (91%), with roughly two-thirds excited by ipsilateral stimuli and one-third by contralateral stimuli. However, the effects of simultaneous stimulation of the two ears suggested that the great majority of efferent units have binaural inputs: the addition of opposite-ear noise or tones, which presented alone were not excitatory, typically enhanced the response to main-ear stimulation. This type of binaural facilitation was strongest among low-CF efferents when the opposite-ear stimuli were tones, and strongest among high-CF units when the opposite-ear stimulus was broadband noise. 5. The binaural facilitation seen using opposite-ear noise both lowered the threshold (by as much as 40 dB) and increased the discharge rate (by as much as 80%) to tones presented in the main ear. Significant facilitation was seen with noise levels as low as 25 dB SPL or tone levels as low as 30 dB SPL. In general, the weaker the response to monaural stimuli, the stronger the binaural facilitation. 6. The facilitatory effects of stimulation with continuous noise could outlast the stimulus. Persistent increases in efferent sensitivity were documented following 10-min exposures to broadband noise at 85-115 dB SPL.

The disengagement of covert attention and the neglect syndrome

Parietal lesions can cause impairment of the ability to disengage attention from an ipsilateral stimulus prior to shifting the focus of attention contralaterally. The present study addresses two main questions concerning the parietal-based disengagement process. First, what is the relationship between the disengagement process, as operationalized by a cued simple reaction-time task, and the neglect syndrome? Second, is there an asymmetry in the roles of the left and right hemisphere in the disengagement of attention? We found a very strong relationship between clinical neglect and impairment of the disengagement operation across patients, and longitudinally, within patients. Furthermore, we found that right-hemisphere lesions cause greater impairment in the disengage process than do left-hemisphere lesions.

Selective attention in an insect auditory neuron

Previous work (Pollack, 1986) showed that an identified auditory neuron of crickets, the omega neuron, selectively encodes the temporal structure of an ipsilateral sound stimulus when a contralateral stimulus is presented simultaneously, even though the contralateral stimulus is clearly encoded when it is presented alone. The present paper investigates the physiological basis for this selective response. The selectivity for the ipsilateral stimulus is a result of the apparent intensity difference of ipsi- and contralateral stimuli, which is imposed by auditory directionality; when simultaneous presentation of stimuli from the 2 sides is mimicked by presenting low- and high-intensity stimuli simultaneously from the ipsilateral side, the neuron responds selectively to the high-intensity stimulus, even though the low-intensity stimulus is effective when it is presented alone. The selective encoding of the more intense (= ipsilateral) stimulus is due to intensity-dependent inhibition, which is superimposed on the cell's excitatory response to sound. Because of the inhibition, the stimulus with lower intensity (i.e., the contralateral stimulus) is rendered subthreshold, while the stimulus with higher intensity (the ipsilateral stimulus) remains above threshold. Consequently, the temporal structure of the low-intensity stimulus is filtered out of the neuron's spike train. The source of the inhibition is not known. It is not a consequence of activation of the omega neuron. Its characteristics are not consistent with those of known inhibitory inputs to the omega neuron.

Enucleation enhances ipsilateral flash evoked responses in the ectostriatum of the zebra finch (Taeniopygia guttata castanotis Gould).

The tectofugal pathway in birds has been reported to process primarily information from the contralateral eye. Although this pathway has access to the contralateral hemisphere by various connections, electrophysiological recordings up to now have failed to demonstrate any excitatory influence of visual stimulation in the higher stations of this pathway. This study is the first to demonstrate an excitatory projection from the ipsilateral eye to the telencephalic projection area of the tectofugal pathway by recordings of visually evoked potentials in the ectostriatum. The excitatory projection probably leads from the eye to the contralateral tectum opticum, then recrosses back to the nucleus rotundus of the ipsilateral side where it reaches the ectostriatum. In normal birds, the ipsilateral stimulus responses in the ectostriatum are smaller in amplitude and have a longer latency than responses to contralateral stimuli. In unilaterally enucleated birds, the ipsilateral response is enhanced in the ectostriatum and can be detected in the nucleus rotundus, too. The results suggest that in normal birds the ipsilateral response is inhibited to a high degree by spontaneous activity of the contralateral eye. Possibly, this counterbalanced inhibition provides a mechanism for weighting information from the left and right eye field in order to ensure adequate processing of stimuli.

Morphology and physiological properties of interneurons in the olfactory midbrain of the crayfish

1. Intracellular recording and staining was used to characterize neurons in the crayfish (Procambarus clarkii) brain that respond to chemical stimuli applied to the major olfactory organs, the antennules. 2. Two distinct morphological types of neurons that have major projections in the olfactory lobes (OLs) of the brain were characterized anatomically (Figs. 1, 2, 3; Table 2) and physiologically (Figs. 4, 5, 6; Table 3). 3. Different individual neurons of one type, with similar 'tree-like' projections in the OLs, have somata distributed in at least 5 different cell body clusters of the brain (Fig. 3) and link different subsets of neuropilar lobes through their distributed arbors (Fig. 1, Table 2). 4. Excitatory, inhibitory and mixed responses were recorded in different neurons when odorant mixtures or individual components of these mixtures were applied to the antennules. Response spectra to individual components were broad and overlapping, but not identical in the neurons tested (Fig. 4; Table 3). Mixture interactions appear to be additive in most of the neurons that we tested, but evidence was obtained for mixture suppression in several cases (Fig. 6). 5. Most of the neurons recorded in this study responded only to stimulation of the ipsilateral antennule (Fig. 5), although subthreshold activity to stimuli applied contralaterally was recorded in several neurons that were strongly excited by ipsilateral stimuli. 6. Chemoresponsive neurons without projections in OL's that have all of their branches confined to the brain, or that project an axon in the circumesophageal connective, are described (Fig. 7).

The inhibition of cat lateral superior olive unit excitatory responses to binaural tone bursts. I. The transient chopper response.

1. The temporal properties of lateral superior olivary (LSO) unit discharges to binaural tone bursts were studied to determine the general time course and statistical properties of these discharges and to provide a basis for extending a point process model of LSO unit monaural discharges to describe their binaural discharges. Single-unit activity was recorded extracellularly from the LSO of the anesthetized cat. The initial transient and the gross temporal features of LSO unit discharges to binaural simultaneous tone bursts are examined in this paper. 2. The poststimulus time (PST) histograms generated by LSO unit discharges to monaural and binaural tone bursts illustrated that the ipsilaterally elicited tone-burst discharges were most strongly inhibited during the initial segment of the binaural response and that the degree of inhibition decreased (i.e., discharge rate increased) as the poststimulus onset time increased. Hence, the contralateral inhibitory effect "adapts" in a manner similar to the ipsilaterally elicited discharges. 3. When the interaural level difference was decreased, the degree of discharge inhibition increased: the period of maximal inhibition spread to shorter and longer poststimulus onset times as the contralateral latency decreased and as the contralateral response magnitude increased. The latency of the inhibitory effect could decrease sufficiently to result in the suppression of the first spike of the ipsilateral discharge. Also, when the binaural stimulus was of sufficient intensity, an increase in spike output, the OFF discharge, was often observed during the last 1-10 ms of the response. 4. It was concluded that the initial and general time course of the binaural response could serve as cues of binaural stimulus level, interaural level differences, and interaural time-of-arrival differences of high-frequency stimuli. The binaural response could be discriminated from a monaural response of similar discharge rate as the former either occurred with shorter latency or, when the first spike was suppressed, with much longer and/or more variable latency than the latter. The gross temporal differences between the monaural and binaural responses could be accounted for in terms of differences in certain gross temporal features (e.g., latency and adaptation) of the ipsilateral and contralateral responses. 5. The effect of stimulating the contralateral ear was not limited to the inhibition of discharges. The timing of a discharge to an ipsilateral stimulus could be perturbed (lengthened) by a contralateral stimulus at levels below that which suppressed the discharge.(ABSTRACT TRUNCATED AT 400 WORDS)