Auditory and tactile frequency representations are co-embedded in modality-defined cortical sensory systems.

Sensory information is represented and elaborated in hierarchical cortical systems that are thought to be dedicated to individual sensory modalities. This traditional view of sensory cortex organization has been challenged by recent evidence of multimodal responses in primary and association sensory areas. Although it is indisputable that sensory areas respond to multiple modalities, it remains unclear whether these multimodal responses reflect selective information processing for particular stimulus features. Here, we used fMRI adaptation to identify brain regions that are sensitive to the temporal frequency information contained in auditory, tactile, and audiotactile stimulus sequences. A number of brain regions distributed over the parietal and temporal lobes exhibited frequency-selective temporal response modulation for both auditory and tactile stimulus events, as indexed by repetition suppression effects. A smaller set of regions responded to crossmodal adaptation sequences in a frequency-dependent manner. Despite an extensive overlap of multimodal frequency-selective responses across the parietal and temporal lobes, representational similarity analysis revealed a cortical "regional landscape" that clearly reflected distinct somatosensory and auditory processing systems that converged on modality-invariant areas. These structured relationships between brain regions were also evident in spontaneous signal fluctuation patterns measured at rest. Our results reveal that multimodal processing in human cortex can be feature-specific and that multimodal frequency representations are embedded in the intrinsically hierarchical organization of cortical sensory systems.

Reciprocal Interactions Between Audition and Touch in Flutter Frequency Perception.

In both audition and touch, sensory cues comprising repeating events are perceived either as a continuous signal or as a stream of temporally discrete events (flutter), depending on the events' repetition rate. At high repetition rates (>100 Hz), auditory and tactile cues interact reciprocally in pitch processing. The frequency of a cue experienced in one modality systematically biases the perceived frequency of a cue experienced in the other modality. Here, we tested whether audition and touch also interact in the processing of low-frequency stimulation. We also tested whether multisensory interactions occurred if the stimulation in one modality comprised click trains and the stimulation in the other modality comprised amplitude-modulated signals. We found that auditory cues bias touch and tactile cues bias audition on a flutter discrimination task. Even though participants were instructed to attend to a single sensory modality and ignore the other cue, the flutter rate in the attended modality is perceived to be similar to that of the distractor modality. Moreover, we observed similar interaction patterns regardless of stimulus type and whether the same stimulus types were experienced by both senses. Combined with earlier studies, our results suggest that the nervous system extracts and combines temporal rate information from multisensory environmental signals, regardless of stimulus type, in both the low- and high temporal frequency domains. This function likely reflects the importance of temporal frequency as a fundamental feature of our multisensory experience.

Auditory Frequency Representations in Human Somatosensory Cortex.

Recent studies have challenged the traditional notion of modality-dedicated cortical systems by showing that audition and touch evoke responses in the same sensory brain regions. While much of this work has focused on somatosensory responses in auditory regions, fewer studies have investigated sound responses and representations in somatosensory regions. In this functional magnetic resonance imaging (fMRI) study, we measured BOLD signal changes in participants performing an auditory frequency discrimination task and characterized activation patterns related to stimulus frequency using both univariate and multivariate analysis approaches. Outside of bilateral temporal lobe regions, we observed robust and frequency-specific responses to auditory stimulation in classically defined somatosensory areas. Moreover, using representational similarity analysis to define the relationships between multi-voxel activation patterns for all sound pairs, we found clear similarity patterns for auditory responses in the parietal lobe that correlated significantly with perceptual similarity judgments. Our results demonstrate that auditory frequency representations can be distributed over brain regions traditionally considered to be dedicated to somatosensation. The broad distribution of auditory and tactile responses over parietal and temporal regions reveals a number of candidate brain areas that could support general temporal frequency processing and mediate the extensive and robust perceptual interactions between audition and touch.

Auditory adaptation improves tactile frequency perception.

Our ability to process temporal frequency information by touch underlies our capacity to perceive and discriminate surface textures. Auditory signals, which also provide extensive temporal frequency information, can systematically alter the perception of vibrations on the hand. How auditory signals shape tactile processing is unclear; perceptual interactions between contemporaneous sounds and vibrations are consistent with multiple neural mechanisms. Here we used a crossmodal adaptation paradigm, which separated auditory and tactile stimulation in time, to test the hypothesis that tactile frequency perception depends on neural circuits that also process auditory frequency. We reasoned that auditory adaptation effects would transfer to touch only if signals from both senses converge on common representations. We found that auditory adaptation can improve tactile frequency discrimination thresholds. This occurred only when adaptor and test frequencies overlapped. In contrast, auditory adaptation did not influence tactile intensity judgments. Thus auditory adaptation enhances touch in a frequency- and feature-specific manner. A simple network model in which tactile frequency information is decoded from sensory neurons that are susceptible to auditory adaptation recapitulates these behavioral results. Our results imply that the neural circuits supporting tactile frequency perception also process auditory signals. This finding is consistent with the notion of supramodal operators performing canonical operations, like temporal frequency processing, regardless of input modality.NEW & NOTEWORTHY Auditory signals can influence the tactile perception of temporal frequency. Multiple neural mechanisms could account for the perceptual interactions between contemporaneous auditory and tactile signals. Using a crossmodal adaptation paradigm, we found that auditory adaptation causes frequency- and feature-specific improvements in tactile perception. This crossmodal transfer of aftereffects between audition and touch implies that tactile frequency perception relies on neural circuits that also process auditory frequency.

A synopsis of current haemophilia care in Hong Kong.

OBJECTIVE: To provide a synopsis of current haemophilia care in Hong Kong. DESIGN: Retrospective survey. SETTING: All haematology units of the Hospital Authority in Hong Kong. PATIENTS: All patients with haemophilia A and haemophilia B. RESULTS: To date, there were 222 mild-to-severe haemophilia patients (192 type A, 30 type B) under regular public care in Hong Kong (43% were considered severe, 33% moderate, and 24% mild), which gave a crude prevalence of 6.8/100 000 male inhabitants. A total of 12.8 million units of Factor VIII and 3 million units of Factor IX were prescribed annually. This amounts to 1.83 units of FVIII per capita of the population, which is comparable to that of other developed countries. Leading causes of mortality were human immunodeficiency virus-related complications (10 cases) and cerebral bleeding (2 cases). The life expectancy of patients with severe haemophilia in Hong Kong is improving; currently the oldest patient is 60 years old. Such improved survival may be due to enhanced factor availability, prompt treatment of bleeding episodes at home, safer factor products, and better antiviral treatment. Primary prophylaxis is the accepted standard of care for severe and moderate cases, and "Factor First" has become hospital policy. However, 12 patients continue to present treatment challenges, due to the documented presence of factor inhibitors. In all, 28, 100, and 14 cases respectively were positive for human immunodeficiency virus, hepatitis C virus, and hepatitis B virus; the youngest patients with the corresponding infections being 28, 13, and 22 years old. Comprehensive care with dedicated physiotherapy, surgical support, and radionucleotide synovectomy may reduce morbidity further. CONCLUSION: A multidisciplinary approach can further improve the future care for haemophilia patients in Hong Kong.

Temporal frequency channels are linked across audition and touch.

Temporal frequency is a fundamental sensory dimension in audition and touch. In audition, analysis of temporal frequency is necessary for speech and music perception; in touch, the spectral analysis of vibratory signals has been implicated in texture perception and in sensing the environment through tools. Environmental oscillations impinging upon the ear are generally thought to be processed independently of oscillations impinging upon the skin. Here, we show that frequency channels are perceptually linked across audition and touch. In a series of psychophysical experiments, we demonstrate that auditory stimuli interfere with tactile frequency perception in a systematic manner. Specifically, performance on a tactile-frequency-discrimination task is impaired when an auditory distractor is presented with the tactile stimuli, but only if the frequencies of the auditory and tactile stimuli are similar. The frequency-dependent interference effect is observed whether the distractors are pure tones or band-pass noise, so an auditory percept of pitch is not required for the effect to be produced. Importantly, distractors that strongly impair frequency discrimination do not interfere with judgments of tactile intensity. This surprisingly specific crosstalk between different modalities reflects the importance of supramodal representations of fundamental sensory dimensions.