Neuroimaging to detect cortical projection of vestibular response to caloric stimulation in young and older adults using functional near-infrared spectroscopy (fNIRS).

Functional near-infrared spectroscopy (fNIRS) is a non-invasive and portable neuroimaging technique. The method uses non-ionizing laser light in the range of red to near-infrared to detect changes in cerebral blood oxygenation. In this study, we used fNIRS to investigate cortical hemodynamic changes in the temporo-parietal and frontal regions during caloric vestibular stimulation. Caloric stimulation has previously been investigated using functional magnetic resonance imaging (fMRI) and positron emission tomography (PET), which serves as a validation of the fNIRS imaging modality toward the measurement of vestibular related brain regions. To date, only a single study has used fNIRS during caloric irrigations, which observed blood volume changes in the temporal-parietal area in healthy younger subjects. In this current study, fNIRS was used to measure cortical vestibular activation in 10 right-handed younger subjects (5 male and 5 female, age 25+/-6 years) and 10 right-handed older subjects (6 male and 4 female, age 74+/-5 years). We investigated both warm (44 °C) and cool (30 °C) unilateral caloric vestibular stimulation. Consistent with previous reports, we found that warm (44 °C) caloric irrigation caused a bilateral activation. In addition, we found that cool (30 °C) caloric irrigation caused contralateral activation of the temporo-parietal area. This study is the first to investigate age effects of the caloric stimulation on brain activity. We found that the older subjects had stronger bilateral effects than the younger subjects. Our results confirm previous fMRI and PET studies that showed cortical activation during caloric vestibular irrigation is dependent on side of irrigation, and temperature of irrigation. Furthermore, our results demonstrate that fNIRS is a viable technique in measuring cortical effects during vestibular tasks.

Space and motion discomfort and abnormal balance control in patients with anxiety disorders.

OBJECTIVE: Previous research suggested that panic disorder with agoraphobia is associated with abnormalities on vestibular and balance function tests. The purpose of this study was to further examine psychiatric correlates of vestibular/balance dysfunction in patients with anxiety disorders and the specific nature of the correlated vestibular abnormalities. The psychiatric variables considered included anxiety disorder versus normal control status, panic disorder versus non-panic anxiety disorder diagnosis, presence or absence of comorbid fear of heights, and degree of space and motion discomfort (SMD). The role of anxiety responses to vestibular testing was also re-examined. METHODS: 104 subjects were recruited: 29 psychiatrically normal individuals and 75 psychiatric patients with anxiety disorders. Anxiety patients were assigned to four subgroups depending on whether or not they had panic disorder and comorbid fear of heights. SMD and anxiety responses were measured by questionnaires. Subjects were examined for abnormal unilateral vestibular hypofunction on caloric testing indicative of peripheral vestibular dysfunction, asymmetric responses on rotational testing as an indicator of an ongoing vestibular imbalance and balance function using Equitest dynamic posturography as an indicator of balance control. Logistic regression was used to establish the association between the psychiatric variables and vestibular or balance test abnormalities. RESULTS: Rotational test results were not significantly related to any of the psychiatric variables. The presence of either panic attacks or fear of heights increased the probability of having caloric hypofunction in a non-additive fashion. SMD and anxiety responses were independently associated with abnormal balance. Among specific posturography conditions, the association with SMD was significant for a condition that involved the balance platform tilting codirectionally with body sway, suggesting an abnormal dependence on somatosensory cues in the control of balance. CONCLUSION: In patients with anxiety disorders, higher SMD is indicative of somatosensory dependence in the control of balance. The absence of both panic and fear of heights reduces the probability of having peripheral vestibular dysfunction. Future research should examine if vestibular rehabilitation can be of value for patients with anxiety disorders complicated by SMD.

Rotational testing.

The natural stimulus for the semicircular canals is rotation of the head, which also might stimulate the otolith organs. Vestibular stimulation usually induces eye movements via the vestibulo-ocular reflex (VOR). The orientation of the subject with respect to the axis of rotation and the orientation of the axis of rotation with respect to gravity together determine which labyrinthine receptors are stimulated for particular motion trajectories. Rotational testing usually includes the measurement of eye movements via a video system but might use a subject's perception of motion. The most common types of rotational testing are whole-body computer-controlled sinusoidal or trapezoidal stimuli during earth-vertical axis rotation (EVAR), which stimulates primarily the horizontal semicircular canals bilaterally. Recently, manual impulsive rotations, known as head impulse testing (HIT), have been developed to assess individual horizontal semicircular canals. Most types of rotational stimuli are not used routinely in the clinical setting but may be used in selected research environments. This chapter will discuss clinically relevant rotational stimuli and several types of rotational testing that are used primarily in research settings.

Panic in otolaryngology patients presenting with dizziness or hearing loss.

This study compared 50 patients presenting to an otolaryngology clinic with a complaint of dizziness and 50 patients presenting with hearing loss on questionnaire measures of panic, phobic avoidance, generalized anxiety, and depression. Clinical and laboratory evaluations of vestibular and audiological complaints were also completed. Twenty percent of the group with dizziness and none of the group with hearing loss reported symptoms that met DSM-III-R criteria for panic disorder. Patients with dizziness and peripheral vestibulopathy had more symptoms of phobic avoidance, generalized anxiety, and depression than patients with confirmed hearing loss.

Panic, agoraphobia, and vestibular dysfunction.

OBJECTIVE: Otoneurological abnormalities have been reported in panic disorder. The purpose of this investigation was to determine the prevalence of such findings in panic disorder with and without agoraphobia and to discern whether vestibular dysfunction was associated with specific symptoms. METHOD: Clinical audiological and vestibular tests were administered to 30 patients with uncomplicated panic disorder (without agoraphobia or with only mild agoraphobia), 29 patients with panic disorder with moderate to severe agoraphobia, 27 patients with anxiety but no history of panic attacks, 13 patients with depressive disorders but no history of anxiety or panic attacks, and 45 normal comparison subjects. Evaluators were blind to subjects' diagnostic group. Quantitative measures of subjects' discomfort with space and motion and of the frequency of certain symptoms between and during panic attacks were obtained. Anxiety state levels were measured during the vestibular tests. RESULTS: Vestibular abnormalities were common in all the groups but most prevalent in the patients with panic disorder with moderate to severe agoraphobia. Vestibular dysfunction was associated with space and motion discomfort and with frequency of vestibular symptoms between, but not during, panic attacks. There were no major differences between the two panic groups in anxiety levels during vestibular testing. There were no significant differences between groups on the audiological component of the test battery. Exploratory data analysis indicated that the constellation of vestibular tests most specific for agoraphobia was one indicating compensated peripheral vestibular dysfunction. CONCLUSIONS: Subclinical vestibular dysfunction, as identified by clinical tests, may contribute to the phenomenology of panic disorder, particularly to the development of agoraphobia in panic disorder patients.

Eye movements in Friedreich's ataxia.

Twenty-four patients with well-documented Friedreich's ataxia underwent quantitative oculomotor testing. A consistent pattern of eye movement abnormalities was observed. This pattern included fixation instability, inaccurate saccades with normal peak velocity, impaired smooth pursuit and optokinetic slow phases, decreased vestibulo-ocular reflex gain, and impaired visual-vestibular interaction. This pattern corresponds to the known pathologic changes of Friedreich's ataxia and can be useful in the differential diagnosis of cerebellar atrophy.

Vestibular compensation in a patient with a cerebellar infarction.

We report the case of a 67-year-old man who suffered a traumatic unilateral peripheral vestibular injury subsequent to an unrelated prior cerebellar infarction that occurred at least 2 years earlier. The patient's clinical course was marked by poor compensation for his peripheral vestibular loss. Four months after his vestibular injury, his symptoms of dizziness had not resolved. He had a spontaneous vestibular nystagmus, and laboratory testing indicated an asymmetric semicircular canal-ocular reflex. The otolith-ocular reflex, tested using off-vertical axis rotation, also was asymmetric but had a preserved modulation component. Visual-vestibular interaction and semicircular canal-otolith interaction were normal. An MRI indicated preservation of the flocculo-nodular lobe but infarction of the pyramis and uvula. Taken together, the findings in this case suggest that despite structural and functional preservation of the flocculo-nodular lobe, an anatomic region often labeled the "vestibulo-cerebellum", a lesion of the cerebellum that can impair CNS compensation for a unilateral peripheral lesion in humans.

Atypical brainstem encephalitis: magnetic resonance imaging and oculographic features.

A 50-year-old woman had primary position upbeating nystagmus, abnormalities of the lower cranial nerves, mild cerebellar signs, and CSF lymphocytosis. CT and MRI showed enlargement of the pons. Eye movement recordings revealed impaired pursuit and optokinetic nystagmus, and visual-vestibular interactions were absent. The patient improved spontaneously.

Dorsal midbrain syndrome: clinical and oculographic findings.

We report clinical and oculographic findings in seven patients with the dorsal midbrain syndrome (Parinaud's syndrome). All presented with limited upward voluntary gaze and convergence nystagmus with attempted upward voluntary gaze. Quantitative analysis of vertical eye movements documented characteristic abnormalities of saccades with relative preservation of reflex eye movements (ie, vestibular, optokinetic, and visual-vestibular). Vertical saccade velocity was only slightly decreased in five patients with tumors, indicating that the vertical burst neurons in the mesencephalic reticular formation and their efferent pathways to the oculomotor neurons were minimally damaged. On the other hand, two patients with probable brainstem encephalitis exhibited marked slowing of vertical saccades, indicating that the burst neurons, or their efferent pathways to the oculomotor neurons, were severely damaged.

Spontaneous remission of paraneoplastic ocular flutter and saccadic intrusions.

We report two women with ocular flutter and saccadic intrusions, documented by electro-oculography, who had complete spontaneous remission of their ocular motor findings prior to the appearance of a primary neoplastic process remote from the nervous system. Transient elevation of blood HVA and VMA levels was detected in one patient who subsequently had breast cancer. These cases indicate that spontaneous remission of saccadic oscillations does not necessarily imply a benign outcome. Patients with this ocular motor abnormality should be followed closely for signs of a remote neoplasm even if initial investigation is negative.

Characteristics of the memory loss of a patient with Wernicke-Korsakoff's syndrome without alcoholism.

The memory loss in alcoholic Wernicke-Korsakoff syndrome has been well characterized. However, it has been suggested that some of the neuropsychological defects seen in these patients are due to frontal lobe dysfunction resulting from chronic alcohol abuse. The present report details the nature and extent of the amnesia in a Wernicke-Korsakoff patient who did not have a history of alcoholism. In spite of her normal performance on measures of frontal lobe function, this patient showed many characteristics similar to those seen in alcoholic Wernicke-Korsakoff syndrome including a graded loss of remote memories and abnormal semantic information processing. Thus, the extent of the "core" features of this amnesic syndrome may be greater than was previously thought.

Semicircular canal-otolith organ interaction during off-vertical axis rotation in humans.

The aim of this study was to examine the interaction of signals from the semicircular canals and the otolith organs during off-vertical axis rotation (OVAR). We recorded horizontal eye position using electro-oculography in 22 young normal human subjects and stimulated the vestibulo-ocular reflex with both constant velocity trapezoids and sinusoidal yaw rotations, using both earth-vertical axis rotation (EVAR) and OVAR. We found that per-rotatory long vestibulo-ocular reflex (VOR) time constants during velocity trapezoids were shorter for OVAR than for EVAR, suggesting a reduction in the efficacy of the velocity storage system during OVAR. However, when we tested with very-low-frequency sinusoids (0.01 Hz and below), the phase lead of the VOR re head velocity was smaller during OVAR than EVAR, suggesting a longer time constant and enhanced efficacy of velocity storage during OVAR. These rotational responses can be explained by two competing influences of signals from the otolith organs, one that diminishes the effectiveness of velocity storage and another that contributes to an estimate of head velocity.

Otolith-ocular testing in human subjects.

Assessment of the otolith-ocular reflex of human subjects involves linear acceleration and/or changes in the orientation of the head with respect to gravity. Several such stimuli are currently under investigation regarding their applicability to the evaluation of patients with dizziness and balance disorders. Discussed in this paper are off-vertical axis rotation, eccentric rotation, pitch and roll rotation, and linear acceleration. For each of these stimuli, basic principles, normative human data, and patient data are described. Although none of these methods are currently established for clinical use, each of them, especially off-vertical axis rotation and linear acceleration, have the potential for developing into a clinically useful method for assessing otolith function in man.

Changes in the horizontal vestibulo-ocular reflex of the rhesus monkey with behavioral and pharmacological alerting.

It is well known that eye movements are influenced by an animal's state of arousal. Alterations in the dynamic characteristics of the horizontal vestibulo-ocular reflex of adolescent rhesus monkeys induced by changes in the animal's state of arousal were studied using linear system analysis employing both single frequency sinusoidal and white noise rotational stimulations. Arousal changes were induced by a behavioral task and/or the administration of amphetamines (0.5 mg/kg). Results indicate that highly alert animals display vestibulo-ocular reflex gains significantly different from less alert animals. Specifically, the gain of the vestibulo-ocular reflex is closer to unity over a wider range of frequencies in more alert animals. These changes were independent of the method used to maintain a high level of arousal.

Time-frequency analysis of postural sway.

Postural sway during quiet stance has been used to characterize the postural control system. Most studies have used center of pressure (COP) measurements and have assumed stationarity, however, recent research has indicated that COP is not stationary. The purpose of this study is to introduce and demonstrate a nonstationary spectral estimation technique to examine the time-varying nature of postural sway. Data from two experiments were used to verify the usefulness of the spectral estimator for the analysis of COP. The first data set contains COP recorded from normal subjects swaying about their ankles in response to a metronome as it was gradually changed from 2 to 1 Hz. The time-frequency distribution reveals time-varying spectral changes corresponding to frequency changes made by the subjects. The second set consists of COP from normal subjects and vestibularly impaired patients standing quietly on a force plate with eyes closed for 100 s. The time-frequency distributions for the COP were estimated for both sets of data. The COP's appear to be nonstationary with the energies at a given frequency modulating through time.

Physical therapy outcomes for persons with bilateral vestibular loss.

OBJECTIVE: The purpose of the study was to assess the efficacy of physical therapy for patients with bilateral vestibular loss. STUDY DESIGN: Retrospective case series. METHODS: Twenty-four patients with a diagnosis of bilateral vestibular loss were identified by a retrospective chart review. Thirteen of the 24 patients met the inclusion criteria of having a moderate or greater loss of vestibular function bilaterally as rated by an otoneurologist based on the patient's vestibular function tests. These patients were treated with a custom-designed physical therapy program for a mean of 4.6 visits over an average period of 3.8 months. Patients completed the Dizziness Handicap Inventory and the Activities-specific Balance Confidence Scale at initial evaluation and discharge. Patients were asked to perform the balance and gait tasks of the Dynamic Gait Index, Sensory Organization Test of computerized dynamic posturography, and the Timed "Up and Go" test at their first and last physical therapy sessions. The number of falls in the previous 4 weeks and the use of an assistive device at initial evaluation and discharge were reported. Composite score, an overall score of clinical outcome, was calculated to determine clinically significant changes in physical performance and subjective information. RESULTS: On a population basis, statistically significant improvement was observed after physical therapy for each of the outcome measures including the composite score (P < .05). Clinically significant changes were demonstrated by 33% to 55% of the patients on the various outcome measures. No change was noted in the patients' risk of falling, their number of falls, and the use of assistive devices. CONCLUSION: Many patients with bilateral vestibular loss benefit from an individualized vestibular physical therapy exercise program based on improved physical function and reduced self-perceived levels of handicap.

Galvanic-induced postural movements as a test of vestibular function in humans.

Galvanic stimulation produces a postural sway and eye movements in humans. Since galvanic currents are thought to exert their effect at the trigger zone of the vestibular nerve, an intact vestibular nerve should be necessary to produce a response. We have used galvanic stimulation in humans to test the hypothesis that intact vestibular nerve fibers are required to obtain a postural away response. Experimental subjects included normal subjects, patients who had undergone resection of an acoustic neuroma, and patients who had undergone vestibular neurectomy and surgical labyrinthectomy. Our results support the hypothesis that an intact vestibular nerve is necessary to produce a response. Moreover, two patients with recurrent vertigo following vestibular neurectomy and labyrinthectomy, who had absent ice-water caloric test responses in the operated ears, were found to have a positive galvanic response. This result suggested that their recurrent vertigo was based on intact residual vestibular nerve fibers. Although previous research has not yielded a routine clinical use for galvanic stimulation, our results suggest that galvanic stimulation of the vestibular system can provide unique and valuable diagnostic information.

Physical therapy for migraine-related vestibulopathy and vestibular dysfunction with history of migraine.

OBJECTIVES/HYPOTHESIS: To assess the efficacy of physical therapy for patients with a diagnosis of migraine-related vestibulopathy (MRV) or vestibular dysfunction with a history of migraine headache. STUDY DESIGN: Retrospective case series METHODS: Thirty-nine patients were identified through a retrospective chart review, 14 with a diagnosis of MRV and 25 with migraine headache. The patients were treated with a custom-designed physical therapy exercise program for a mean of 4.9 visits over a mean duration of 4 months. Patients completed the Dizziness Handicap Inventory (DHI), the Activities-Specific Balance Confidence Scale (ABC), and the Dynamic Gait Index (DGI), reported the number of falls they had experienced in the past 4 weeks, and rated the severity of their dizziness on an analogue scale of 0 to 100 at initial evaluation and at discharge. RESULTS: Significant differences were seen before and after therapy in each of the outcome measures used. The average decrease in DHI score was 12 points (P < .01). ABC scores increased an average of 14 points (P < .01). Subjects increased their DGI scores an average of 4 points (P < .01). The number of patients reporting more than one fall decreased by 78% at discharge. (P < .05). Baseline symptoms of dizziness decreased an average of 11 points (P < .05). CONCLUSIONS: Patients with MRV and migraine headache demonstrated improvement in physical performance measures and self-perceived abilities after vestibular physical therapy.

Past history of otitis media and balance in four-year-old children.

OBJECTIVES/HYPOTHESIS: To obtain normative data for a population of children 4 years of age with respect to standard vestibular and balance test protocols and to determine, in the absence of concurrent middle ear effusion (MEE), the possible changes caused by a history of recurrent or persistent MEE. STUDY DESIGN: Comparative studies of the results of vestibular and balance tests in a cohort of young children with and without a history of MEE. METHODS: Seventy-one children, 4 years of age, with a well-documented history since early infancy regarding the presence or absence of MEE were evaluated using pneumatic otoscopy, tympanometry, audiometry, and vestibular and balance (rotational and moving platform posturography) tests. For the results of the vestibular and balance tests, comparisons were made between the group of 31 children (43.7%) without and the group of 40 children (56.3%) with a history of recurrent or persistent MEE, when a positive disease history was defined as at least a 10% cumulative percentage of time with MEE between early infancy and time of testing. RESULTS: When compared with children with a negative history of significant MEE, children with a positive history had a lower average gain to a rotational stimulus of 0.1 Hz, 150 degrees/s (0.57 vs. 0.44; P = .007). There were no significant differences between groups with respect to other measures. CONCLUSIONS: These results suggest that a history of recurrent or persistent MEE affects the vestibular and/or balance function of 4-year-old children when tested in the absence of a concurrent episode of MEE. The possible sequelae of the disease should be weighed in future considerations of early intervention for MEE.

Attention influences sensory integration for postural control in older adults.

This study investigated the influence of attention on the sensory integration component of postural control in young and older adults. Eighteen young and 18 older healthy subjects performed information-processing tasks during different postural challenge conditions. Postural conditions included seated, standing on a firm surface, standing on a sway-referenced floor, and standing on a sway-referenced floor while viewing a sway-referenced scene. During each condition, reaction time (RT) was measured during two simple and one inhibitory RT tasks. For the inhibitory task, the time required to inhibit an action was derived, termed the inhibitory time (IT). Performing a RT task was associated with increased postural sway in older subjects, but not in young subjects. The greatest influence of RT task on sway of older subjects was found during the sway-referenced floor/sway-referenced scene condition. Conversely, postural condition had an influence on RT task performance in both young and older subjects. The IT was increased in both young and older subjects only during the sway-referenced floor/scene condition. These results suggest that the sensory integration component of postural control in particular seems to require attention. Further, our data suggest that attentional processes related to inhibitory control are engaged when sensory integration requirements are high.