Sensory Discrimination Thresholds Research Articles

The role of stimulus periodicity on spinal cord stimulation-induced artificial sensations in rodents

Objective. Sensory feedback is critical for effectively controlling brain-machine interfaces and neuroprosthetic devices. Spinal cord stimulation (SCS) is proposed as a technique to induce artificial sensory perceptions in rodents, monkeys, and humans. However, to realize the full potential of SCS as a sensory neuroprosthetic technology, a better understanding of the effect of SCS pulse train parameter changes on sensory detection and discrimination thresholds is necessary. Approach. Here we investigated whether stimulation periodicity impacts rats’ ability to detect and discriminate SCS-induced perceptions at different frequencies. Main results. By varying the coefficient of variation (CV) of interstimulus pulse interval, we showed that at lower frequencies, rats could detect highly aperiodic SCS pulse trains at lower amplitudes (i.e. decreased detection thresholds). Furthermore, rats learned to discriminate stimuli with subtle differences in periodicity, and the just-noticeable differences from a highly aperiodic stimulus were smaller than those from a periodic stimulus. Significance. These results demonstrate that the temporal structure of an SCS pulse train is an integral parameter for modulating sensory feedback in neuroprosthetic applications.

Deficits in Auditory and Visual Sensory Discrimination Reflect a Genetic Liability for Psychosis and Predict Disruptions in Global Cognitive Functioning.

Sensory discrimination thresholds (i.e., the briefest stimulus that can be accurately perceived) can be measured using tablet-based auditory and visual sweep paradigms. These basic sensory functions have been found to be diminished in patients with psychosis. However, the extent to which worse sensory discrimination characterizes genetic liability for psychosis, and whether it is related to clinical symptomatology and community functioning remains unknown. In the current study we compared patients with psychosis (PSY; N=76), their first-degree biological relatives (REL; N=44), and groups of healthy controls (CON; N=13 auditory and visual/N=275 auditory/N=267 visual) on measures of auditory and visual sensory discrimination, and examined relationships with a battery of symptom, cognitive, and functioning measures. Sound sweep thresholds differed among the PSY, REL, and CON groups, driven by higher thresholds in the PSY compared to CON group, with the REL group showing intermediate thresholds. Visual thresholds also differed among the three groups, driven by higher thresholds in the REL versus CON group, and no significant differences between the REL and PSY groups. Across groups and among patients, higher thresholds (poorer discrimination) for both sound and visual sweeps strongly correlated with lower global cognitive scores. We conclude that low-level auditory and visual sensory discrimination deficits in psychosis may reflect genetic liability for psychotic illness. Critically, these deficits relate to global cognitive disruptions that are a hallmark of psychotic illnesses such as schizophrenia.

Distinguishing between nociceptive and neuropathic components in chronic low back pain using behavioural evaluation and sensory examination

BackgroundDiagnosis of chronic low back pain (CLBP) is traditionally predicated on identifying underlying pathological or anatomical causes, with treatment outcomes modest at best. Alternately, it is suggested that identification of underlying pain mechanisms with treatments targeted towards specific pain phenotypes may yield more success. Differentiation between nociceptive and neuropathic components of CLBP is problematic; evidence suggests that clinicians fail to identify a significant neuropathic component in many CLBP patients. The painDETECT questionnaire (PDQ) was specifically developed to identify occult but significant neuropathic components in individuals thought to have predominantly nociceptive pain. MethodsUsing the PDQ, we classified 50 CLBP patients into two distinct groups; those with predominantly nociceptive pain (Group 1) and those with a significant neuropathic component (Group 2). We characterised these two distinct CLBP sub-groups using a) questionnaire-based behavioural evaluation measuring pain-related function and quality of life, pain intensity and psychological well-being and b) sensory examination, using two-point and tactile threshold discrimination. ObjectiveWe sought to determine if differences in the pain phenotype of each CLBP sub-group would be reflected in sensory and behavioural group profiles. ResultsWe report that Group 1 and Group 2 sub-groups demonstrate unique clinical profiles with significant differences in sensory tactile discrimination thresholds and in a wide range of behavioural domains measuring pain intensity, disability and psychological well-being. ConclusionWe have demonstrated distinct clinical profiles for CLBP patient sub-groups classified by PDQ. Our results give diagnostic confidence in using the PDQ to characterise two distinct pain phenotypes in a heterogeneous CLBP population.

No difference in cross-modal attention or sensory discrimination thresholds in autism and matched controls

Autism has been associated with abnormalities in sensory and attentional processing. Here, we assessed these processes independently in the visual and auditory domains using a visual contrast-discrimination task and an auditory modulation-depth discrimination task. To evaluate changes in sensory function by attention, we measured behavioral performance (discrimination accuracy) when subjects were cued to attend and respond to the same stimulus (frequent valid cue) or cued to attend to one stimulus and respond to the non-cued stimulus (infrequent invalid cue). The stimuli were presented at threshold to ensure equal difficulty across participants and groups. Results from fifteen high-functioning adult individuals with autism and fifteen matched controls revealed no significant differences in visual or auditory discrimination thresholds across groups. Furthermore, attention robustly modulated performance accuracy (performance was better for valid than invalid cues) in both sensory modalities and to an equivalent extent in both groups. In conclusion, when using this well-controlled method, we found no evidence of atypical sensory function or atypical attentional modulation in a group of high functioning individuals with clear autism symptomatology.

Variations in tongue-palate swallowing pressures when swallowing xanthan gum-thickened liquids.

Thickened liquids are frequently recommended to reduce the risk of aspiration in patients with oropharyngeal dysphagia. Although it has previously been reported that tongue-palate pressures increase when swallowing spoon-thick and semi-solid consistencies compared to thin liquids, relatively little is known about how swallowing behaviors differ when swallowing liquids of nectar- or honey-thick consistency. Furthermore, previous studies have primarily used starch-based thickeners, and little is known about swallowing behaviors with xanthan gum-thickened liquids, which have recently been introduced for dysphagia management. In this study, we measured variations in tongue-palate pressures during the swallowing of liquids thickened to apparent viscosities of 190, 250, and 380 mPa s at 50/s using increasing concentrations of xanthan gum (0.5, 0.63 and 0.87 w/w%). The viscosity differences between these nectar- and honey-thick stimuli were confirmed to exceed sensory perceptual discrimination thresholds. Data were collected from 78 healthy adults in two sex-balanced age-groups (young; mature) and compared to reference values obtained during water swallowing. The results confirm that increased amplitudes of tongue-palate pressure were used when swallowing the thickened liquid stimuli, compared to swallows of water, and for the honey-thick liquid compared to the two nectar-thick liquids. Age-related reductions were seen in tongue strength but not in swallowing pressures, which fell below 40 % of maximum isometric pressure values. Thus, the use of xanthan gum-thickened liquids is unlikely to tax the swallowing system in terms of tongue pressure generation requirements, even in seniors with reduced maximum isometric tongue pressure measures.

Noradrenergic modulation of behavioral odor detection and discrimination thresholds in the olfactory bulb

The mammalian main olfactory bulb (MOB) receives a significant noradrenergic input from the locus coeruleus. Norepinephrine (NE) is involved in the acquisition of conditioned odor preferences in neonatal animals and in some species-specific odor-dependent behaviors. Thus far, the role of NE in odor processing in adult rats remains less studied. We investigated the role of noradrenergic modulation in the MOB on odor detection and discrimination thresholds using behavioral and computational modeling approaches. Adult rats received bilateral MOB injections of vehicle, NE (0.1-1000 microM), noradrenergic receptor antagonists and NE + receptor antagonists combined. NE infusion improved odor detection and discrimination as a function of NE and odor concentration. The effect of NE on detection and discrimination magnitude at any given odor concentration varied in a non-linear function with respect to NE concentration. Receptor antagonist infusion demonstrated that alpha1 receptor activation is necessary for the modulatory effect of NE. Computational modeling showed that increases in the strength of alpha1 receptor activation leads to improved odor signal-to-noise ratio and spike synchronization in mitral cells that may underlie the behaviorally observed decrease of detection and discrimination thresholds. Our results are the first to show that direct infusion of NE or noradrenergic receptor antagonists into a primary sensory network modulates sensory detection and discrimination thresholds at very low stimulus concentrations.

Laryngeal sensory deficits in patients with chronic cough and paradoxical vocal fold movement disorder

Although the diagnostic accuracy of paradoxical vocal fold movement disorder and chronic cough has improved, the underlying pathophysiology remains relatively unknown. We hypothesize that one potential etiological factor in these patients is an aberrant laryngeal sensory response and sought to determine if respiratory retraining in addition to antireflux therapy alters this aberrant response. Retrospective, outcomes. Sixteen patients who had been on at least 3 months of twice-daily proton pump inhibitors with no subjective improvement in their primary complaint of cough, self-reported symptoms of gastroesophageal and laryngopharyngeal reflux, and concurrent paradoxical vocal fold movement (PVFM) were included in the current study. In addition to continuing twice daily pharmacological therapy, subjects underwent a course of respiratory retraining. Outcome measures including the Reflux Symptom Index (RSI), transnasal flexible laryngoscopy, and laryngopharyngeal sensory discrimination thresholds were obtained prior to and following a course of respiratory retraining. Mean bilateral laryngeal sensory response improved significantly after combined respiratory retraining and aggressive proton pump inhibitor therapy (P = .01). In addition, mean RSI score decreased significantly following treatment (P = .02). Specifically, 13 of 16 patients experienced improved sensory response, corresponding with patient reports of improved PVFM symptoms following treatment. Aberrant laryngeal sensation was identified in patients with PVFM and chronic cough. This response, however, normalized following a limited course of respiratory retraining, corresponding with improved patient symptoms.

The safety of flexible endoscopic evaluation of swallowing with sensory testing (FEESST): an analysis of 500 consecutive evaluations.

We assessed the safety of a new office or bedside method of evaluating both the motor and sensory components of swallowing called flexible endoscopic evaluation of swallowing with sensory testing (FEESST). FEESST combines the established endoscopic evaluation of swallowing with a technique that determines laryngopharyngeal sensory discrimination thresholds by endoscopically delivering air-pulse stimuli to the mucosa innervated by the superior laryngeal nerve. Endoscopic assessment of laryngopharyngeal sensory capacity followed by endoscopic visualization of deglutition was prospectively performed 500 times in 253 patients with dysphagia over a 2.5-year period in a tertiary care center. The patients had a variety of underlying diagnoses, with stroke and chronic neurological disease predominating (n = 155). To determine the safety of FEESST, the presence of epistaxis, airway compromise, and significant changes in heart rate before and after the evaluation were assessed. Patients were also asked to rate the level of discomfort of the examination; 498 evaluations were completed. There were three instances of epistaxis that were self-limited. There were no cases of airway compromise. There were no significant differences in heart rate between pre- and posttest measurements (p > 0.05). Eighty-one percent of patients noted either no discomfort or mild discomfort as a result of the examination. In conclusion, FEESST is a safe method of evaluating dysphagia in the tertiary care setting and may also have application for the chronic care setting.

FEESST: a new bedside endoscopic test of the motor and sensory components of swallowing.

We here introduce an office or bedside method of evaluating both the motor and sensory components of swallowing, called fiberoptic endoscopic evaluation of swallowing with sensory testing (FEESST). FEESST combines the established endoscopic evaluation of swallowing with a technique that determines laryngopharyngeal (LP) sensory discrimination thresholds by endoscopically delivering air pulse stimuli to the mucosa innervated by the superior laryngeal nerve. Endoscopic assessment of LP sensory capacity followed by endoscopic visualization of deglutition was prospectively performed 148 times on 133 patients with dysphagia over an 8-month period. The patients had a variety of underlying diagnoses, with stroke and chronic neurologic disease predominating (n = 94). Subsequent to LP sensory testing, a complete dysphagia evaluation was conducted. Various food and liquid consistencies were dyed green, and attention was paid to their management throughout the pharyngeal stage of swallowing. Evidence of latent swallow initiation, pharyngeal pooling and/or residue, laryngeal penetration, laryngeal aspiration, and/or reflux was noted. Recommendations for therapeutic intervention were based on information obtained during the FEESST and often involved the employment of compensatory swallowing strategies, modification of the diet or its presentation, placement on non-oral feeding status, and/or referral to other related specialists. All patients successfully completed the examination. In 111 of the evaluations (75%), severe (>6.0 mm Hg air pulse pressure [APP]) unilateral or bilateral LP sensory deficits were found. With puree consistencies, 31% of evaluations with severe deficits, compared to 5% of evaluations with either normal sensitivity or moderate (4.0 to 6.0 mm Hg APP) LP sensory deficits, displayed aspiration (p < .001, chi2 test). With puree consistencies, 69% of evaluations with severe deficits, compared to 24% with normal or moderate deficits, displayed laryngeal penetration (p < .001, chi2 test). FEESST allows the clinician to obtain a comprehensive bedside assessment of swallowing that is performed as the initial swallowing evaluation for the patient with dysphagia.

Fiberoptic endoscopic evaluation of swallowing with sensory testing (FEESST) in healthy controls.

The purpose of this study was to introduce a new method of bedside assessment of both the motor and sensory components of swallowing called fiberoptic endoscopic evaluation of swallowing with sensory testing (FEESST). This approach combines the established bedside endoscopic swallowing evaluation with a more recently described technique that allows objective determination of laryngopharyngeal (LP) sensory discrimination thresholds by delivering air pulse stimuli to the mucosa innervated by the superior laryngeal nerve via a flexible endoscope. A prospective study was conducted of FEESST in 20 healthy control subjects, mean age of 34 +/- 11 years. LP sensory thresholds were defined as either normal (< 4.0 mmHg air pulse pressure [APP]), moderate deficit (4.0-6.0 mmHg APP), or severe deficits (> 6.0 mmHg APP). Subsequent to LP sensory testing, food of varying consistencies, mixed with green food coloring, was given and attention was paid to spillage, laryngeal penetration, pharyngeal residue, aspiration, and reflux. Therapeutic maneuvers such as postural changes and airway protection techniques were performed on each subject to determine if the assessed swallowing parameters were affected by maneuvers. All patients completed the study; all had normal LP sensory discrimination thresholds (2.9 +/- 0.7 mmHg APP). There were no instances of spillage, laryngeal penetration, or aspiration. Two of 20 subjects had pharyngeal residue and 2 of 20 had reflux. Institution of therapeutic maneuvers resulted in a predictable change in the endoscopic view of the laryngopharyngeal anatomy. FEESST provides comprehensive, objective sensory and motor information about deglutition in the bedside setting and might have implications for the bedside diagnosis and management of patients with dysphagia.

Effects of Aging on Sensitivity of the Pharyngeal and Supraglottic Areas

As one ages, sensory discrimination in the oral cavity progressively diminishes, and dysphagia and aspiration are more likely to occur. Whether similar age-related laryngopharyngeal (LP) sensory abnormalities exist and contribute to dysphagia and aspiration is unknown. The purpose of this study was to determine if sensory discrimination in the area of the laryngopharynx innervated by the superior laryngeal nerve diminishes with increasing age. By applying a previously described device and technique that utilized endoscopically delivered air pulse stimulation of the anterior wall of the pyriform sinus, sensory discrimination can be reliably determined. LP sensory discrimination testing was performed in 80 healthy adults 23–87 years of age, with a mean age of 47 ± 20 years. There were 60 men and 20 women. The test subjects were divided into 3 age groups, 20–40, 41–60, and ≥61. For the entire population studied, average LP sensory discrimination thresholds were 2.60 ± 0.56 mm Hg air pulse pressure (APP). In general, there was a progressive increase in sensory discrimination threshold with each decade of life. A correlation analysis revealed that there were significant increases in pressure thresholds with advancing age (r = 0.62, P <0.0001). For subjects 20–40 years, average threshold was 2.06 ± 0.20 mm Hg APP, for the 41–60 age group, 2.45 ± 0.34 mm Hg APP, and for subjects ≥61, 2.97 ± 0.78 mm Hg APP. Thresholds for the ≥61 group were significantly different from those for the 20–40 and the 41–60 groups ( P <0.05). Progressive diminution in LP sensitivity with increasing age might be a contributing factor in the development of dysphagia and aspiration in the elderly.

Sensory discrimination in the larynx and hypopharynx

The traditional approach to evaluating swallowing disorders has focused on upper aerodigestive tract motor function. The evaluation of the sensory apparatus in the larynx and pharynx as part of the workup of dysphagia has heretofore not been addressed. The purpose of this work is to discuss a new, noninvasive method to measure sensory discrimination in the supraglottic larynx and hypopharynx. An air pulse, of precise duration and pressure, was delivered through a flexible fiberoptic telescope to the submucosally situated superior laryngeal nerve along the anterior wall of the pyriform sinus. Three hundred sixty trials were conducted in 30 healthy adults. The average sensory discrimination was 2.24 ± 0.28 mm Hg. Brief air-pulse stimulation is a safe, reliable means of determining supraglottic and hypopharyngeal sensory discrimination thresholds. (Otolaryngol Head Neck Surg 1997;116:331-4.)

Sensory discrimination in the larynx and hypopharynx.

The traditional approach to evaluating swallowing disorders has focused on upper aerodigestive tract motor function. The evaluation of the sensory apparatus in the larynx and pharynx as part of the workup of dysphagia has heretofore not been addressed. The purpose of this work is to discuss a new, noninvasive method to measure sensory discrimination in the supraglottic larynx and hypopharynx. An air pulse, of precise duration and pressure, was delivered through a flexible fiberoptic telescope to the submucosally situated superior laryngeal nerve along the anterior wall of the pyriform sinus. Three hundred sixty trials were conducted in 30 healthy adults. The average sensory discrimination was 2.24 +/- 0.28 mm Hg. Brief air-pulse stimulation is a safe, reliable means of determining supraglottic and hypopharyngeal sensory discrimination thresholds.

Supraglottic and pharyngeal sensory abnormalities in stroke patients with dysphagia.

Dysphagia and aspiration are two devastating sequelae of stroke, accounting for nearly 40,000 deaths from aspiration pneumonia each year in the United States. While motor deficits in the larynx and pharynx are thought responsible for dysphagia and aspiration in stroke patients, no prior study has evaluated whether these patients also have sensory deficits. The aim of this study was to evaluate the sensory capacity of the laryngopharynx (LP) in supratentorial or brain stem stroke patients who presented with dysphagia. Fifteen stroke patients (mean age, 66.7 +/- 13.8 [SD] years) were prospectively evaluated by means of our previously described method whereby air pulse stimuli were delivered via a flexible fiberoptic telescope to the mucosa innervated by the superior laryngeal nerve. There were 15 age-matched controls. No LP sensory deficits were found in any of the age-matched controls. In all stroke patients studied, either unilateral (n = 9) or bilateral (n = 6) sensory deficits were identified. Deficits were defined as either a moderate impairment in sensory discrimination thresholds (3.5 to 6.0 mm Hg) or a severe sensory impairment (> 6.0 mm Hg). These sensory discrimination thresholds were significantly greater than in age-matched controls (7.05 +/- 0.17 mm Hg for the supratentorial group and 6.05 +/- 1.22 mm Hg for the infratentorial group versus 2.61 +/- 0.69 mm Hg for the controls). Among patients with unilateral deficits, sensory thresholds were moderately to severely elevated in all 9 cases on the affected side compared with the unaffected side (p < .01, Fisher's exact test). Moreover, the sensory thresholds of the unaffected side were not significantly different from those of age-matched controls (2.51 +/- 0.25 mm Hg versus 2.61 +/- 0.69 mm Hg, respectively). All 6 patients with bilateral deficits had severe impairments. The results of an outcome assessment in 13 of 15 patients revealed that 2 out of 5 patients with moderate LP sensory impairment and 5 out of 8 with severe impairment developed aspiration. Our results show for the first time that stroke patients with dysphagia have significant sensory deficits in the LP and that these impairments are likely to contribute to the development of aspiration.

Air Pulse Quantification of Supraglottic and Pharyngeal Sensation: A New Technique

There are no published studies evaluating the sensory capacity of the region innervated by the superior laryngeal nerve. A normal sensory capacity is important in this area, since hypesthesia or anesthesia of the pharynx and supraglottic larynx may result in dysphagia and aspiration. This often occurs after stroke or after ablative surgery of the pharynx and larynx. Evaluating the efficacy of restorative procedures for supraglottic and pharyngeal sensation is dependent on defining and quantifying the sensory deficit. We have developed a new, noninvasive method to measure sensation in the pharynx and supraglottic larynx. A puff of air--of precisely controlled duration and pressure--was delivered via a flexible telescope to the anterior wall of the pyriform sinus. Surface sensibility was determined according to the psychophysical method of limits by varying air pressure while holding puff duration constant. We conducted 204 trials in 20 healthy adults. The average sensory discrimination threshold was 2.09 +/- 0.15 mm Hg. An intraclass correlation revealed excellent consistency (R = .80). There was no statistically significant difference between the right and left sides. Brief air pulse stimulation is an easy, relatively safe, and reliable method of determining supraglottic and pharyngeal sensory discrimination thresholds.

Sensory discrimination thresholds with cutaneous nerve volleys in the cat.

Sensory discrimination thresholds with cutaneous nerve volleys in the cat.

Comparison of sensory discrimination thresholds with muscle and cutaneous nerve volleys in the cat.

Comparison of sensory discrimination thresholds with muscle and cutaneous nerve volleys in the cat.