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PubMed2005

How important is lateral masking in visual search?

Five experiments are presented, providing empirical support of the hypothesis that the sensory phenomenon of lateral masking may explain many well-known visual search phenomena that are commonly assumed to be governed by cognitive attentional mechanisms. Experiment I showed that when the same visual arrays are used in visual search and in lateral masking experiments, the factors (1) number of distractors, (2) distractor density, and (3) search type (conjunction vs disjunction) have the same effect on search times as they have on lateral masking scores. Experiment II showed that when the number of distractors and eccentricity is kept constant in a search task, the effect of reducing density (which reduces the lateral masking potential of distractors on the target) is to strongly reduce the disjunction-conjunction difference. In experiment III, the lateral masking potential of distractors on a target was measured with arrays that typically yield asymmetric search times in visual search studies (a Q among Os vs. an O among Qs). The lateral masking scores showed the same asymmetry. Experiment IV was a visual search study with such asymmetric search arrays in which the number of distractors and eccentricity was kept constant, while manipulating density. Reducing density (i.e., reducing lateral masking) produced a strong reduction of the asymmetry effect. Finally in experiment V, we showed that the data from experiment IV cannot be explained due to a difference between a fine and a coarse grain attentional mechanism. Taken together with eye movement data and error scores from experiment II and with similar findings from the literature, these results suggest that the sensory mechanism of lateral masking could well be a very important (if not the main) factor causing many of the well-known effects that are traditionally attributed to higher level cognitive or attentional mechanisms in visual search.

Attention↗
PubMed1989

Human laterality reversal auditory evoked potentials: stimulation by reversing the interaural delay of dichotically presented continuous click trains.

Long-latency responses to bidirectional reversals in the laterality of a sound image were recorded from vertex with left and right earlobe references simultaneously. Laterality reversal stimuli with regular ISIs of 3 sec were obtained by alternating between +1 msec and -1 msec the interaural delay (ID) of dichotically presented 70 c/sec continuous click trains. Monaural presentation of this temporal modulation did not evoke any potential or any sensation whereas, when dichotically presented, the same ID modulation was perceived as laterality reversals. Evoked potentials from 9 right-handed volunteers with normal hearing were evaluated. The recorded laterality reversal auditory evoked potentials (LRAEPs) consisted, characteristically, of a negative and a positive wave with average peak latencies of 160 msec and 260 msec, respectively. Statistical analysis indicated significant dependence of the response parameters on the direction of the sound image shifts, but the laterality of the earlobe reference did not prove to be important. The appropriateness of the stimulus parameters employed was discussed from the viewpoint of dynamic systems analysis. By contrasting with the monaural auditory off-responses recorded from the same subjects, it was demonstrated that the laterality reversal responses we obtained did not seem to be non-specific 'rest-to-motion' responses to any change in the acoustic background. Similarities and differences between these laterality reversal responses and various ERP components in the same latency range were also discussed. It is concluded that the LRAEPs introduced in this communication can be used in assessing the functional integrity and studying the dynamics of the neurophysiological system that accomplishes sound lateralization using cues of interaural time disparity (ITD).

Acoustic Stimulation↗
PubMed1985

Lateralized rewarding brain stimulation affects forepaw preference in rats.

Rats trained to reach for food pellets into a narrow tubular feeder consistently prefer to perform this stereotype instrumental movement with either the left or right forepaw. In 16 rats with established handedness electrodes were implanted into both lateral hypothalami. The animals were rewarded by intracranial self stimulation (ICSS, 300 msec, 50 Hz, 20-60 microA) for reaching into a modified feeder for a plastic ball operandum, the movement of which between the bottom and entrance of the feeder was monitored by mechanical contacts. The rats readily continued to reach when ICSS was delivered immediately after the photoelectrically detected reach or after the displacement of the operandum. Most rats learned in a single session to modify the movement when ICSS delivery was made contingent upon holding the operandum between the bottom and entrance of the feeder for 256 or 512 msec. The efficiency of reaching (ratio of successful reaches to all reaches) decreased with increasing holding time; only a few animals were able to master a 1024 msec delay. Reaching was supported by ICSS of either lateral hypothalamus. Whereas in 8 rats the strongly expressed forepaw preference was not changed by lateralized ICSS, in 8 latently ambidextrous animals stimulation of the lateral hypothalamus ipsilateral to the preferred forepaw increased reaching with the normally non-preferred forepaw from 15% to 60%. Stimulation of the lateral hypothalamus contralateral to the preferred forepaw did not change the preference. The preference shift was equally well expressed in simple and difficult versions of the task. It is concluded that lateralization of motivational influences can be reflected in the asymmetry of the neural mechanisms processing the lateralized sensory signals and/or elaborating the lateralized motor output.

Animals↗
PubMed2005

fsi zebrafish show concordant reversal of laterality of viscera, neuroanatomy, and a subset of behavioral responses.

Asymmetries in CNS neuroanatomy are assumed to underlie the widespread cognitive and behavioral asymmetries in vertebrates. Studies in humans have shown that the laterality of some cognitive asymmetries is independent of the laterality of the viscera; discrete mechanisms may therefore regulate visceral and neural lateralization. However, through analysis of visceral, neuroanatomical, and behavioral asymmetries in the frequent-situs-inversus (fsi) line of zebrafish, we show that the principal left-right body asymmetries are coupled to certain brain asymmetries and lateralized behaviors. fsi fish with asymmetry defects show concordant reversal of heart, gut, and neuroanatomical asymmetries in the diencephalon. Moreover, the neuroanatomical reversals in reversed fsi fish correlate with reversal of some behavioral responses in both fry and adult fsi fish. Surprisingly, two behavioral asymmetries do not reverse, suggesting that at least two separable mechanisms must influence functional lateralization in the CNS. Partial reversal of CNS asymmetries may generate new behavioral phenotypes; supporting this idea, reversed fsi fry differ markedly from their normally lateralized siblings in their behavioral response to a novel visual feature. Revealing a link between visceral and brain asymmetry and lateralized behavior, our studies help to explain the complexity of the relationship between the lateralities of visceral and neural asymmetries.

Analysis of Variance↗
PubMed1997

Identification of retinal ganglion cells projecting to the lateral hypothalamic area of the rat.

The objective of the present study was to identify the retinal ganglion cells projecting to the lateral hypothalamic area of the rat. The retinohypothalamic tract has been divided into a medial and a lateral component on anatomical and developmental grounds. The medial component projects to the suprachiasmatic nucleus and adjacent structures such as the anterior hypothalamic and retrochiasmatic areas. The lateral component terminates in the lateral hypothalamic are dorsal to the supraoptic nucleus. Injections of the retrograde tracer FluoroGold were made into the retinorecipient region of the lateral hypothalamic area and retinal whole mounts were immunohistochemically processed for retrogradely labeled retinal ganglion cells. With FluoroGold injections confined to the lateral hypothalamic area, retrogradely labeled retinal ganglion cells are located almost exclusively in the superior temporal quadrant of the retina. Their size and morphology indicates that they are a homogeneous subset of type III cells, but a definitive classification would require a more complete fill of dendritic arbors than is available in our retrograde material. In contrast, injections involving fibers of passage in the optic tract, or centered in the medial terminal nucleus of the accessory optic system, label cells distributed across the entire retinal surface. Unlike the retinal ganglion cells projecting to the suprachiasmatic nucleus [Moore et al., J. Comp. Neurol., 352 (1995) 351-366], the cells labeled after restricted lateral hypothalamic injections are not distributed evenly across the retinal surface. The difference in location of the retinal ganglion cells projecting to the lateral hypothalamic area supports the view that this retinohypothalamic projection is anatomically and functionally distinct from the projection to the suprachiasmatic nucleus and adjacent medial hypothalamus.

Animals↗
PubMed1998

Inter-hemispheric lateralization of event related potentials; motoric versus non-motoric cortical activity.

To study hemispheric lateralization of cortical potentials associated with motoric and non-motoric function, cortical activity was recorded accompanying either finger extension or saccadic eye movements in a contingent negative variation (CNV) paradigm. Subjects viewed computer-generated pacing stimuli, presented in the left visual hemi-field, and were instructed to either initiate or inhibit a motor response following an imperative signal. Motoric lateralization was assessed by means of the lateralized readiness potential (LRP). In addition, a measure complementary to the LRP was introduced to investigate non-motoric lateralization (NML). Contralateral inter-hemispheric lateralization was evident in the LRP preceding finger movement, but was absent prior to eye movements. However, pre-saccadic cortical response profiles did exhibit a right hemispheric, non-motoric lateralization (NML) during stimulus presentation. Comparable non-motoric lateralization was found for finger extension. Results of the present study suggest that non-motoric lateralization may be a contributing factor to the frequently reported inter-hemispheric asymmetry preceding self-initiated saccadic eye movements. Results of the present study also suggest that the latter may be related to a covert shift of visuospatial attention toward the saccadic target. Associated shifts of attention are suppressed in a CNV paradigm, where attentional focus is primarily on the CNV stimulus during the pre-saccade period.

Adult↗
PubMed1998

Footedness is a better predictor than is handedness of emotional lateralization.

A tremendous amount of experimental work has attempted to identify reliable behavioural predictors of cerebral lateralization. Preferred handedness has been the most popular predictor, but some recent reports suggest that preferred footedness may serve as a more accurate predictor of functional laterality, especially in the left-handed population. The present study sought to test this claim by selectively recruiting individuals with either 'crossed' lateral preferences (right-handed and left-footed or left-handed and right-footed) or 'uncrossed' lateral preferences (right-handed and right-footed or left-handed and left-footed). Lateralization of emotional perception was assessed with two blocks of the dichotic Emotional Words Test (EWT), and lateral preference for both handedness and footedness was assessed using self-report questionnaires. Ear advantage on the dichotic task varied significantly with preferred foot (P=0.003), but not with preferred hand. Cerebral lateralization may be more related to footedness than to other lateral preferences.

Adult↗
PubMed2003

Salivary testosterone is related to both handedness and degree of linguistic lateralization in normal women.

The aim of this study was to test the hypothesis that individual differences in testosterone (T) are associated with different patterns of linguistic lateralization and hand preference. Twenty left-handed (LH) and 19 right-handed (RH) women filled in a handedness questionnaire and performed a consonant-vowel dichotic listening test (DL-CV). Salivary T was measured by radioimmunoassay (RIA). LH women showed significantly lower mean salivary T than RH women. T levels were negatively correlated with the absolute value of the DL laterality index. Subjects with right ear advantage (REA) were classified into strongly and weakly lateralized following Wexler et al. method (Brain Lang. 13 (1981) 13). When taking into account hand preference, a pattern emerged in that RH-strongly lateralized and LH-weakly lateralized women showed similar T levels. The lowest level appeared for LH-strongly lateralized women and the highest for RH-weakly lateralized women, being significantly different from each other. The results are discussed in terms of several theories that have proposed a link between testosterone and cerebral lateralization.

Adult↗
PubMed2000

Sound lateralization and interaural discrimination. Effects of brainstem infarcts and multiple sclerosis lesions.

Subjects with brainstem lesions due to either an infarct or multiple sclerosis (MS) underwent two types of binaural testing (lateralization testing and interaural discrimination) for three types of sounds (clicks and high and low frequency narrow-band noise) with two kinds of interaural differences (level and time). Two major types of abnormalities were revealed in the lateralization performances: perception of all stimuli, regardless of interaural differences (time and/or level) in the center of the head (center-oriented), or lateralization of all stimuli to one side or the other of the head (side-oriented). Similar patterns of abnormal lateralization (center-oriented and side-oriented) occurred for MS and stroke patients. A subject's pattern of abnormal lateralization testing was the same regardless of the type of stimulus or type of interaural disparity. Lateralization testing was a more sensitive test than interaural discrimination testing for both types of subjects. Magnetic resonance image (MRI) scanning in three orthogonal planes of the brainstem was used to detect lesions. A semi-automated algorithm superimposed the auditory pathway onto each MRI section. Whenever a lesion overlapped the auditory pathway, some binaural performance was abnormal and vice versa. Given a lateralization test abnormality, whether the pattern was center-oriented or side-oriented was mainly determined by lesion site. Center-oriented performance was principally associated with caudal pontine lesions and side-oriented performance with lesions rostral to the superior olivary complex. For lesions restricted to the lateral lemniscus and/or inferior colliculus, whether unilateral or bilateral, just noticeable differences (JNDs) were nearly always abnormal, but for caudal pontine lesions JNDs could be normal or abnormal. MS subjects were more sensitive to interaural time delays than interaural level differences particularly for caudal pontine lesions, while stroke patients showed no differential sensitivity to the two kinds of interaural differences. These results suggest that neural processing of binaural stimuli is multilevel and begins with independent interaural time and level analyzers in the caudal pons.

Adult↗
PubMed2001

A segmentation-based and partial-volume-compensated method for an accurate measurement of lateral ventricular volumes on T(1)-weighted magnetic resonance images.

Lateral ventricular volumes based on segmented brain MR images can be significantly underestimated if partial volume effects are not considered. This is because a group of voxels in the neighborhood of lateral ventricles is often mis-classified as gray matter voxels due to partial volume effects. This group of voxels is actually a mixture of ventricular cerebro-spinal fluid and the white matter and therefore, a portion of it should be included as part of the lateral ventricular structure. In this note, we describe an automated method for the measurement of lateral ventricular volumes on segmented brain MR images. Image segmentation was carried in combination of intensity correction and thresholding. The method is featured with a procedure for addressing mis-classified voxels in the surrounding of lateral ventricles. A detailed analysis showed that lateral ventricular volumes could be underestimated by 10 to 30% depending upon the size of the lateral ventricular structure, if mis-classified voxels were not included. Validation of the method was done through comparison with the averaged manually traced volumes. Finally, the merit of the method is demonstrated in the evaluation of the rate of lateral ventricular enlargement.

Brain↗
PubMed2002

Magnetic oscillatory responses to lateralization changes of natural and artificial sounds in humans.

Oscillatory signals in human magnetoencephalogram were investigated as correlates of cortical network activity in response to sound lateralization changes. Previously, we found lateralized presentations of a monosyllabic word to elicit posterior temporo-parietal gamma-band activity, possibly reflecting synchronization of neuronal assemblies in putative auditory dorsal stream areas. In addition, beta activity was decreased over sensorimotor regions, suggesting the activation of motor networks involved in orientating. The present study investigated responses to lateralization changes of both a barking dog sound and a distorted noise to test whether beta desynchronization would depend on the sound's relevance for orientating. Eighteen adults listened passively to 900 samples of each sound in separate location mismatch paradigms with midline standards and both right- and left-lateralized deviants. Lateralized distorted noises were accompanied by enhanced spectral amplitude at 58-73 Hz over right temporo-parietal cortex. Left-lateralized barking dog sounds elicited right and right-lateralized sounds elicited bilateral temporo-parietal spectral amplitude increases at approximately 77 Hz. This replicated the involvement of posterior temporo-parietal areas in auditory spatial processing. Only barking dog sounds, but not distorted noises, gave rise to 30 Hz desynchronization over contralateral sensorimotor areas, parieto-frontal gamma coherence increases and beta coherence reductions between sensorimotor and prefrontal sensors. Apparently passive listening to lateralized natural sounds with a potential biological relevance led to an activation of motor networks involved in the automatic preparation for orientating. Parieto-frontal coherence increases may reflect enhanced coupling of networks involved in the integration of auditory spatial and motor processes.

Acoustic Stimulation↗
PubMed2002

Language lateralization in monozygotic twin pairs concordant and discordant for handedness.

An unexpectedly high percentage of monozygotic twin pairs is discordant for handedness. Some of these twins show mirror-imaging of several ectodermally derived features. Both features of discordant left-right asymmetry may be caused by relatively late monozygotic twinning, when the original embryo has already lost its bilateral symmetry. Language lateralization is related to handedness and may therefore also be altered during the development of embryological asymmetry in some monozygotic twins. Language lateralization was measured with functional MRI in 12 monozygotic twin pairs who were concordant for handedness and in 13 monozygotic twin pairs discordant for handedness. Lateralization indices were calculated from individual language activation patterns. Correlations were calculated to test intra-pair resemblance for language lateralization. The intra-pair correlation for language lateralization was significant in the handedness-concordant group, but not in the handedness-discordant group. In the handedness-discordant group, five twin pairs were also discordant for cerebral dominance; the other twin pairs of discordant handedness exhibited remarkable similarity in language lateralization. The high intra-pair correlation for language lateralization in the handedness-concordant twins suggests a genetic basis for language lateralization. However, in monozygotic twin pairs of discordant handedness, discordance for language dominance occurs in a significant number of twins. Discordant language dominance may be caused by a relatively late time of splitting of the original embryo, which disrupts the normal development of left-right asymmetry.

Female↗
PubMed2002

Nutritional issues and supplements in amyotrophic lateral sclerosis and other neurodegenerative disorders.

PURPOSE OF REVIEW: Aggressive nutritional intervention has become a cornerstone of treatment for many patients with neuromuscular diseases, in particular, motor neuron disease. Malnutrition is a common problem among patients with amyotrophic lateral sclerosis. Over the past decade, the recognition of nutrition as an independent, prognostic factor for survival and disease complications in amyotrophic lateral sclerosis has illustrated the importance of individualized nutritional management in symptomatic treatment. Paramount issues for nutritional management in amyotrophic lateral sclerosis include caloric supplementation, the diagnosis/treatment of dysphagia, and the timing/safety/efficacy of percutaneous endoscopic gastrostomy placement. RECENT FINDINGS: In addition, many amyotrophic lateral sclerosis patients self-medicate with a variety of vitamins, herbs, and other dietary supplements. Outcome-based research for the use of nutraceuticals and functional foods in the treatment and prevention of amyotrophic lateral sclerosis and other neuromuscular diseases is in its early stages. In the past year, however, several interesting papers have been published that lend support to the use of dietary supplements as primary treatments for amyotrophic lateral sclerosis and other motor neuron disorders. SUMMARY: Common or overlapping etiologies in disparate neurodegenerative diseases have led to the promise that optimal nutritional care and the appropriate use of dietary supplements in amyotrophic lateral sclerosis will have implications for the nutritional management of other degenerative conditions such as Parkinson's, Alzheimer's, and Huntington's disease. Furthermore, evidence supporting the efficacy of dietary supplements in amyotrophic lateral sclerosis may lend clues to the treatment of other neuromuscular disorders such as the muscular dystrophies.

Amyotrophic Lateral Sclerosis↗
PubMed2006

Is language lateralization in temporal lobe epilepsy patients related to the nature of the epileptogenic lesion?

PURPOSE: Early acquired lesions are considered to be a risk factor for atypical language lateralization in epilepsy, whereas developmental lesions are not. Hippocampal sclerosis (HS) can be understood as an early, acquired lesion, whereas developmental tumors (DT) are thought to originate in utero. We assessed whether language lateralization differs between these groups of temporal lobe epilepsy patients. METHODS: We used 3-Tesla functional MRI (fMRI) to assess 41 patients (16 DT, 25 HS) and 50 controls, performing a noun-verb-generation task. fMRI data were processed by using SPM2. A laterality index (LI) was calculated based on the number of activated voxels in left- and right-sided frontal lobe language areas. Atypical lateralization was considered if the index was < or = 0.2. RESULTS: Patients had a lower LI (0.42 +/- 0.5) than controls (0.6 +/- 0.3; p < or = 0.05), but the LI was not different between DT (0.44 +/- 0.5) and HS patients (0.43 +/- 0.4; p = 0.9). The frequency of atypical lateralization was increased in patients (27%) compared with controls (8%) but was similar in both patient groups (DT, 31%; HS, 24%). HS patients had an earlier onset and longer duration of epilepsy and a higher frequency of significant antecedent events (p < or = 0.05). CONCLUSIONS: Patients with TLE demonstrate a deviation toward atypical language lateralization. However, language lateralization was not different between patients with presumably acquired lesions compared with patients with developmental pathology. This suggests that the nature of the temporal lobe lesion does not influence overall language lateralization.

Adult↗
PubMed1993

Lateral hypothalamic lesions alter baroreceptor-evoked inhibition of rat supraoptic vasopressin neurones.

1. Previous electrophysiological studies on rat hypothalamic supraoptic nucleus neurones have demonstrated that both the activation of peripheral baroreceptors (induced by a brief rise in arterial pressure consequent to an intravenous injection of an alpha-adrenergic agonist, metaraminol) and electrical stimulation in the diagonal band of Broca evokes a GABA-mediated postsynaptic inhibition which selectively involves the phasic-firing (putative vasopressin-secreting) neuronal population. Although baroreceptor-triggered inhibitions are abolished after diagonal band lesions, anatomical data support the hypothesis that the GABAergic neurones mediating both the baroreflex and electrically induced inhibitions are not located in the diagonal band, but rather in the lateral hypothalamus adjacent to the supraoptic nucleus. To determine the validity of this hypothesis, excitotoxic lesions were placed in the lateral hypothalamus and their effects on both baroreceptor- and diagonal band-evoked inhibitions were evaluated. 2. Male Long-Evans rats were initially anaesthetized with intraperitoneal pentobarbitone, stereotaxically injected with an excitotoxin (ibotenic acid) or vehicle into the lateral hypothalamus on the left side and allowed to recover. Three or more days later, animals were again anaesthetized with pentobarbitone and the ventral surface of their hypothalamus was exposed for electrophysiological recording of neurones in the left supraoptic nucleus. In all injected animals, extracellular recordings from antidromically identified, phasically firing supraoptic neurones were evaluated for their response to activation of peripheral baroreceptors and to electrical stimulation in the diagonal band. 3. Increases in arterial pressure sufficient to activate peripheral baroreceptors were achieved by intravenous bolus infusions of metaraminol (10 micrograms/10 microliters). In vehicle control animals (n = 6), the activity of 34/39 neurones was inhibited by baroreceptor activation. In lesion control animals (n = 13) similar inhibitions were observed from 60/65 neurones. In the lateral hypothalamic lesioned group (n = 7), the activity of only 12/34 neurones were inhibited by similar elevations in blood pressure. 4. Ibotenic acid lesions in the lateral hypothalamus also disrupted the responsiveness of supraoptic neurones to electrical stimulation in the diagonal band. Whereas diagonal band stimulation in vehicle control and lesion control rats reduced the excitability in 7/9 cells and 15/19 cells respectively, only 1/7 cells responded in the lesioned animals. 5. Lesions having a significant effect on the responsiveness of vasopressin-secreting neurones to baroreceptor activation extended laterally towards the nucleus of the lateral olfactory tract, dorsally into the striatum and medially to the fornix.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2005

Lesional location of lateral medullary infarction presenting hiccups (singultus).

BACKGROUND: Hiccups are an infrequent result of lateral medullary infarction. Their importance may be underestimated and they can cause distress, exhaustion, and aspiration. Hiccups in lateral medullary infarction remain poorly understood OBJECTIVE: To evaluate the relation between the lesional loci of lateral medullary infarction and hiccups. METHODS: 51 patients with lateral medullary infarction were investigated by magnetic resonance imaging within three days of the onset of infarction. Seven of the 51 patients developed hiccup. RESULTS: All patients with hiccups had middle level lateral medullary lesions, including two with lower level lesions and four with upper level lesions. In the middle level lateral medullary lesions, dorsolateral lesions were most often involved. All patients with lateral medullary infarction presenting with hiccups also had vertigo, dizziness, nausea, vomiting, and dysphagia. CONCLUSIONS: The observations suggest that middle level and dorsolateral lesion locations in lateral medullary infarction frequently induce hiccups.

Adult↗
PubMed1996

Interactions of gastric vagal and peripheral nerves on single neurons of lateral hypothalamus in the cat.

Extracellularly recorded unitary responses in the lateral hypothalamus were evaluated in anesthetized cats during electrical stimulation of the gastric branches of the ventral and dorsal vagal trunks, the T9 intercostal nerve, and the common peroneal nerve (L6-S2). These nerves were stimulated with single or paired (10-ms interval) pulses of 300-500 microA for 0.3 ms at a frequency of 0.5 Hz. The latency of the evoked lateral hypothalamic responses after stimulation of the gastric vagal branches (373 +/- 39.8 ms; means +/- SD) was significantly longer than the latencies after intercostal nerve (62 +/- 17.0 ms) or common peroneal nerve (109 +/- 29.3 ms) stimulation. Convergence of gastric vagal input from the proximal stomach and peripheral nerves (PNs) on single neurons in the lateral hypothalamus was observed. Ninety-two percent of the lateral hypothalamic neurons tested that responded to gastric vagal stimulation also received inputs from the T9 intercostal nerve. Seventy-seven percent of the lateral hypothalamic gastric vagally evoked unitary responses received convergent inputs from the intercostal nerve and the common peroneal nerve. A condition-test paradigm was applied to determine the time course of convergent gastric and PN input on single lateral hypothalamic neurons. The test revealed that stimulation of the T9 intercostal nerve had a more pronounced effect than common peroneal nerve stimulation on the lateral hypothalamic neurons that receive gastric vagal input. The results demonstrated that gastric vagal afferent and PN inputs converge onto single lateral hypothalamic neurons and suggested that the central processing of visceral input from the stomach can be substantially affected by peripheral nerve stimulation.

Animals↗
PubMed2000

Lateralized tinnitus studied with functional magnetic resonance imaging: abnormal inferior colliculus activation.

Tinnitus, the perception of sound in the absence of external stimuli, is a common and often disturbing symptom that is not understood physiologically. This paper presents an approach for using functional magnetic resonance imaging (fMRI) to investigate the physiology of tinnitus and demonstrates that the approach is effective in revealing tinnitus-related abnormalities in brain function. Our approach as applied here included 1) using a masking noise stimulus to change tinnitus loudness and examining the inferior colliculus (IC) for corresponding changes in activity, 2) separately considering subpopulations with particular tinnitus characteristics, in this case tinnitus lateralized to one ear, 3) controlling for intersubject differences in hearing loss by considering only subjects with normal or near-normal audiograms, and 4) tailoring the experimental design to the characteristics of the tinnitus subpopulation under study. For lateralized tinnitus subjects, we hypothesized that sound-evoked activation would be abnormally asymmetric because of the asymmetry of the tinnitus percept. This was tested using two reference groups for comparison: nontinnitus subjects and nonlateralized tinnitus subjects. Binaural noise produced abnormally asymmetric IC activation in every lateralized tinnitus subject (n = 4). In reference subjects (n = 9), activation (i.e., percent change in image signal) in the right versus left IC did not differ significantly. Compared with reference subjects, lateralized tinnitus subjects showed abnormally low percent signal change in the IC contralateral, but not ipsilateral, to the tinnitus percept. Consequently, activation asymmetry (i.e., the ratio of percent signal change in the IC ipsilateral versus contralateral to the tinnitus percept) was significantly greater in lateralized tinnitus subjects as compared with reference subjects. Monaural noise also produced abnormally asymmetric IC activation in lateralized tinnitus subjects. Two possible models are presented to explain why IC activation was abnormally low contralateral to the tinnitus percept in lateralized tinnitus subjects. Both assume that the percept is associated with abnormally high ("tinnitus-related") neural activity in the contralateral IC. Additionally, they assume that either 1) additional activity evoked by sound was limited by saturation or 2) sound stimulation reduced the level of tinnitus-related activity as it reduced the loudness of (i.e., masked) the tinnitus percept. In summary, this work demonstrates that fMRI can provide objective measures of lateralized tinnitus and tinnitus-related activation can be interpreted at a neural level.

Acoustic Stimulation↗