Biology subjects

Ezquerra-Romano, I.

Publications and source records attributed to Ezquerra-Romano, I..

3 recordsLinked to original sources

bioRxiv2023

Challenging a classical theory of sensory specificity: inconsistency and instability of thermosensitive spots

Thermal sensitivity is not uniform across the skin, and is particularly high in small ([~]1mm2) regions termed thermosensitive spots. These spots are thought to reflect the anatomical location of specialised thermosensitive nerve endings from single primary afferents. Thermosensitive spots provide foundational support for "labelled line" or specificity theory of sensory perception, which state that different sensory qualities are transmitted by separate and specific neural pathways. This theory predicts a highly stable relation between repetitions of a thermal stimulus and the resulting sensory quality, yet these predictions have rarely been tested systematically. Here we present the qualitative, spatial and repeatability properties of 334 thermosensitive spots on the dorsal forearm sampled across 4 separate sessions. In line with previous literature, we found that spots associated with cold sensations (112 cold spots, 34%) were more frequent than spots associated with warm sensations (41 warm spots, 12%). Still more frequent (165 spots, 49%) were spots that elicited inconsistent sensations when repeatedly stimulated by the same temperature. Remarkably, only 13 spots (4%) conserved their position between sessions. Overall, we show unexpected inconsistency of both the perceptual responses elicited by spot stimulation and of spot locations across time. These observations call to revise the traditional view that thermosensitive spots reflect the location of individual thermosensitive, unimodal primary afferents serving as specific labelled lines for corresponding sensory qualities. New & NoteworthyThermosensitive spots are clustered rather than randomly distributed, and have highest density near the wrist. Surprisingly, we found that thermosensitive spots elicit inconsistent sensory qualities and are unstable over time. Our results question the widely believed notion that thermosensitive spots reflect the location of individual thermoreceptive, unimodal primary afferents, that serve as labelled lines for corresponding sensory qualities.

neuroscience↗

bioRxiv2023

Cortical cellular encoding of thermotactile integration

Recent evidence suggests that primary sensory cortical regions play a role in the integration of information from multiple sensory modalities. How primary cortical neurons integrate multisensory information is unclear, partly because multisensory interactions in the cortex are typically weak or modulatory. To address this question, we take advantage of the robust representation of thermal (cooling) and tactile stimuli in mouse forepaw primary somatosensory cortex (fS1). Using a thermotactile detection task, we show that the perception of threshold level cool or tactile information is enhanced when they are presented simultaneously compared to presentation alone. To investigate the cortical correlates of thermotactile integration, we performed in vivo extracellular recordings from fS1 during unimodal and bimodal stimulation of the forepaw. Unimodal stimulation evoked thermal- or tactile- specific excitatory and inhibitory responses of fS1 neurons. The most prominent features of bimodal, thermotactile stimulation are the recruitment of unimodally silent fS1 neurons, non-linear integration features and a change in the response dynamics to favor longer response durations. Together, we identify quantitative and qualitative changes in cortical encoding that may underlie the improvement in perception of multisensory, thermotactile surfaces during haptic exploration.

neuroscience↗

bioRxiv2022

Cold stimulation without touch: a method for perceptual and neurophysiological studies of thermal processing and multimodal interactions

BackgroundThermal and tactile stimuli are transduced by different receptor classes. However, mechano- and thermo-sensitive afferents interact at spinal and supraspinal levels. Yet, most studies on responses to cooling stimuli are confounded by mechanical contact, making these interactions difficult to isolate. Methods for precise control of non-mechanical thermal stimulations remain challenging, particularly in the cold range. New MethodWe developed a non-tactile, focal, temperature-controlled, multi-purpose cooling stimulator. This method controls the exposure of a target skin region to a dry-ice source. Using a thermal camera to monitor skin temperature, and adjusting the source-skin distance accordingly, we could deliver non-tactile cooling stimuli with customisable profiles, for studying different aspects of cold sensation. ResultsTo validate our method, we measured absolute and relative thresholds for cold sensation without mechanical contact in 13 human volunteer participants, using the method of limits. We found that the absolute cold detection threshold was 32.71{degrees}C {+/-} 0.88 {degrees}C. This corresponded to a threshold relative to each participants baseline skin temperature of -1.08 {degrees}C {+/-} 0.37 {degrees}C. Comparisons with Existing MethodOur method allows cooling stimulation without the confound of mechanical contact, in a controllable and focal manner. ConclusionsWe report a non-contact cooling stimulator and accompanying control system. We used this to measure cold thresholds in the absence of confounding touch. Our method enables more targeted studies of both cold sensory pathways, and of cold-touch interactions. HighlightsMost studies on cold sensation fail to control for concomitant tactile input. A method to deliver non-tactile cooling stimuli was developed. The method combines dry ice, a thermal camera, and motorised stages. The method delivers rapid ramps and feedback-controlled pulses. Thresholds for contactless cold perception were estimated in humans.

neuroscience↗