Sub-threshold cross-modal sensory interaction in the thalamus: lemniscal auditory response in the medial geniculate nucleus is modulated by somatosensory stimulation

Cross-Modal Interaction and Integration Through Stimulus-Specific Adaptation in the Thalamic Reticular Nucleus of Rats

Stimulus-specific adaptation (SSA), defined as a decrease in responses to a common stimulus that only partially generalizes to other rare stimuli, is a widespread phenomenon in the brain that is believed to be related to novelty detection. Although cross-modal sensory processing is also a widespread phenomenon, the interaction between the two phenomena is not well understood. In this study, the thalamic reticular nucleus (TRN), which is regarded as a hub of the attentional system that contains multi-modal neurons, was investigated. The results showed that SSA existed in an interactive oddball stimulation, which mimics stimulation changes from one modality to another. In the bimodal integration, SSA to bimodal stimulation was stronger than to visual stimulation alone but similar to auditory stimulation alone, which indicated a limited integrative effect. Collectively, the present results provide evidence for independent cross-modal processing in bimodal TRN neurons.

Cross-modal modulation of cell activity by sound in first-order visual thalamic nucleus

Cross-modal auditory influence on cell activity in the primary visual cortex emerging at short latencies raises the possibility that the first-order visual thalamic nucleus, which is considered dedicated to unimodal visual processing, could contribute to cross-modal sensory processing, as has been indicated in the auditory and somatosensory systems. To test this hypothesis, the effects of sound stimulation on visual cell activity in the dorsal lateral geniculate nucleus were examined in anesthetized rats, using juxta-cellular recording and labeling techniques. Visual responses evoked by light (white LED) were modulated by sound (noise burst) given simultaneously or 50-400 ms after the light, even though sound stimuli alone did not evoke cell activity. Alterations of visual response were observed in 71% of cells (57/80) with regard to response magnitude, latency, and/or burst spiking. Suppression predominated in response magnitude modulation, but de novo responses were also induced by combined stimulation. Sound affected not only onset responses but also late responses. Late responses were modulated by sound given before or after onset responses. Further, visual responses evoked by the second light stimulation of a double flash with a 150-700 ms interval were also modulated by sound given together with the first light stimulation. In morphological analysis of labeled cells projection cells comparable to X-, Y-, and W-like cells and interneurons were all susceptible to auditory influence. These findings suggest that the first-order visual thalamic nucleus incorporates auditory influence into parallel and complex thalamic visual processing for cross-modal modulation of visual attention and perception.

Chemometric Modeling of Coffee Sensory Notes through Their Chemical Signatures: Potential and Limits in Defining an Analytical Tool for Quality Control

Aroma is a primary hedonic aspect of a good coffee. Coffee aroma quality is generally defined by cup tasting, which however is time-consuming in terms of panel training and alignment and too subjective. It is challenging to define a relationship between chemical profile and aroma sensory impact, but it might provide an objective evaluation of industrial products. This study aimed to define the chemical signature of coffee sensory notes, to develop prediction models based on analytical measurements for use at the control level. In particular, the sensory profile was linked with the chemical composition defined by HS-SPME-GC-MS, using a chemometric-driven approach. The strategy was found to be discriminative and informative, identifying aroma compounds characteristic of the selected sensory notes. The predictive ability in defining the sensory scores of each aroma note was used as a validation tool for the chemical signatures characterized. The most reliable models were those obtained for woody, bitter, and acidic properties, whose selected volatiles reliably represented the sensory note fingerprints. Prediction models could be exploited in quality control, but compromises must be determined if they are to become complementary to panel tasting.

Robust Subthreshold Cross-modal Modulation of Auditory Response by Cutaneous Electrical Stimulation in First- and Higher-order Auditory Thalamic Nuclei

Conventional extracellular recording has revealed cross-modal alterations of auditory cell activities by cutaneous electrical stimulation of the hindpaw in first- and higher-order auditory thalamic nuclei (Donishi et al., 2011). Juxta-cellular recording and labeling techniques were used in the present study to examine the cross-modal alterations in detail, focusing on possible nucleus and/or cell type-related distinctions in modulation. Recordings were obtained from 80 cells of anesthetized rats. Cutaneous electrical stimulation, which did not elicit unit discharges, i.e., subthreshold effects, modulated early (onset) and/or late auditory responses of first- (64%) and higher-order nucleus cells (77%) with regard to response magnitude, latency and/or burst spiking. Attenuation predominated in the modulation of response magnitude and burst spiking, and delay predominated in the modulation of response time. Striking alterations of burst spiking took place in higher-order nucleus cells, which had the potential to exhibit higher propensities for burst spiking as compared to first-order nucleus cells. A subpopulation of first-order nucleus cells showing modulation in early response magnitude in the caudal domain of the nucleus had larger cell bodies and higher propensities for burst spiking as compared to cells showing no modulation. These findings suggest that somatosensory influence is incorporated into parallel channels in auditory thalamic nuclei to impose distinct impacts on cortical and subcortical sensory processing. Further, cutaneous electrical stimulation given after early auditory responses modulated late responses. Somatosensory influence is likely to affect ongoing auditory processing at any time without being coincident with sound onset in a narrow temporal window.

Listening to another sense: somatosensory integration in the auditory system

Conventionally, sensory systems are viewed as separate entities, each with its own physiological process serving a different purpose. However, many functions require integrative inputs from multiple sensory systems and sensory intersection and convergence occur throughout the central nervous system. The neural processes for hearing perception undergo significant modulation by the two other major sensory systems, vision and somatosensation. This synthesis occurs at every level of the ascending auditory pathway: the cochlear nucleus, inferior colliculus, medial geniculate body and the auditory cortex. In this review, we explore the process of multisensory integration from (1) anatomical (inputs and connections), (2) physiological (cellular responses), (3) functional and (4) pathological aspects. We focus on the convergence between auditory and somatosensory inputs in each ascending auditory station. This review highlights the intricacy of sensory processing and offers a multisensory perspective regarding the understanding of sensory disorders.

An audiometric study of the effects of paraspinal stimulation on hearing acuity in human subjects - understanding the Harvey Lillard phenomenon

Background

The founder of chiropractic, Daniel David Palmer, constructed a model of causation of disease based on his seminal experience with a patient, Harvey Lillard, who lost his hearing at the instant of injuring his upper back, but had his hearing restored suddenly 17 years later after receiving spinal manipulation. Palmer’s model of disease causation, that of displaced vertebrae impinging on spinal nerves and thereby disrupting the innervation of dependent organs, was in fact incongruent with what was known at the time about human neuroanatomy and neurophysiology. The current study proposes and tests an alternative hypothesis: that increased afferent input from paraspinal muscles attenuates the central transmission of auditory information.

Methods

Between September 13 and November 13, 2013, forty healthy young adults were recruited and randomly divided into two cohorts: one receiving successive trials of sham TENS, and the second receiving sham and then authentic TENS. During the administration of sham and authentic TENS to the upper thoracic spine, hearing acuity was measured to determine perception thresholds at the frequencies normally tested clinically.

Results

In the first cohort, there were no differences in perception thresholds in the first and second trials of sham TENS, speaking to the reliability of the testing process. In the second cohort, there were no significant differences in perception thresholds during sham and authentic TENS.

Conclusions

Within the constraints of the current study design, including demographic characteristics and TENS parameters, there was no evidence that innocuous afferent input to upper thoracic paraspinal muscles modulated thresholds of audibility.

Diverse subthreshold cross-modal sensory interactions in the thalamic reticular nucleus: implications for new pathways of cross-modal attentional gating function

Our attention to a sensory cue of a given modality interferes with attention to a sensory cue of another modality. However, an object emitting various sensory cues attracts attention more effectively. The thalamic reticular nucleus (TRN) could play a pivotal role in such cross-modal modulation of attention given that cross-modal sensory interaction takes place in the TRN, because the TRN occupies a highly strategic position to function in the control of gain and/or gating of sensory processing in the thalamocortical loop. In the present study cross-modal interactions between visual and auditory inputs were examined in single TRN cells of anesthetised rats using juxta-cellular recording and labeling techniques. Visual or auditory responses were modulated by subthreshold sound or light stimuli, respectively, in the majority of recordings (46 of 54 visual and 60 of 73 auditory cells). However, few bimodal sensory cells were found. Cells showing modulation of the sensory response were distributed in the whole visual and auditory sectors of the TRN. Modulated cells sent axonal projections to first-order or higher-order thalamic nuclei. Suppression predominated in modulation that took place not only in primary responses but also in late responses repeatedly evoked after sensory stimulation. Combined sensory stimulation also evoked de-novo responses, and modulated response latency and burst spiking. These results indicate that the TRN incorporates sensory inputs of different modalities into single cell activity to function in sensory processing in the lemniscal and non-lemniscal systems. This raises the possibility that the TRN constitutes neural pathways involved in cross-modal attentional gating.

Associations of volatile compounds with sensory aroma and flavor: the complex nature of flavor

Attempts to relate sensory analysis data to specific chemicals such as volatile compounds have been frequent. Often these associations are difficult to interpret or are weak in nature. Although some difficulties may relate to the methods used, the difficulties also result from the complex nature of flavor. For example, there are multiple volatiles responsible for a flavor sensation, combinations of volatiles yield different flavors than those expected from individual compounds, and the differences in perception of volatiles in different matrices. This review identifies some of the reasons sensory analysis and instrumental measurements result in poor associations and suggests issues that need to be addressed in future research for better understanding of the relationships of flavor/aroma phenomena and chemical composition.