Vibrotactile amplitude discrimination capacity parallels magnitude changes in somatosensory cortex and follows Weber’s Law

Abstract

In this study, we investigated the changes in perceptual metrics of amplitude discrimination that were observed in ten healthy human subjects with increasing intensities of stimulation. The ability to perceive differences in vibrotactile amplitude changed systematically with increasing stimulus magnitude (i.e., followed Weber's Law) in a near linear fashion (R (2) = 0.9977), and the linear fit determined by the amplitude discrimination task predicted the subjects' detection thresholds. Additionally, the perceptual metrics correlated well with observations from a previously reported study in which measures of SI cortical activity in non-human primates (squirrel monkeys) evoked by different amplitudes of vibrotactile stimulation were obtained (Simons et al. in BMC Neurosci 6:43, 2005). Stimuli were delivered simultaneously to two different skin sites (D2 and D3), enabling a method for the relatively rapid acquisition of the data. Stability and robustness of the measure, its rapid acquisition, and its apparent relationship with responses previously observed in SI cortex, led to the conclusion that deviations from the baseline values observed in the obtained perceptual metric could provide a useful indicator of cerebral cortical health.

Centrally-mediated sensory information processing is impacted with increased alcohol consumption in college-aged individuals

“…This modification significantly altered the ability of a subject to perceive the actual difference among the two stimuli in a predictable and quantifiable fashion. As a result, these methods could be viewed as a reliable indicator of the influence of adapting stimuli on the central nervous system response, as changes in the peripheral response are not significantly changed at these short stimulus durations (for discussion see Francisco et al, 2008Francisco et al, , 2011Tannan et al, 2007Tannan et al, , 2008Tommerdahl et al, 2007aTommerdahl et al, , 2007bTommerdahl et al, , 2008Zhang et al, 2011aZhang et al, , 2011b. These findings may have value as a method of assessing cortical dysfunction in relation to unhealthy alcohol use across the spectrum from low-level risk drinking to overt alcohol dependence.…”

“…In other words, abnormal processing of the conditioning stimulus allows better task performance, and these results, along with prior reports, imply that this performance is a result of decreased CNS function in subjects who consume higher amounts of alcohol. The reduction of the adaptation metric with increased alcohol consumption of alcohol in the college-aged population has not been previously reported, although such reductions in other subject populations have been observed previously, and the neurobiological basis of short-term adaptation has been discussed extensively (Folger et al, 2008;Francisco et al, 2008;Tannan et al, 2005Tannan et al, , 2007Tannan et al, , 2008Tommerdahl et al, 2007Tommerdahl et al, , 2010aZhang et al, 2009Zhang et al, , 2011aZhang et al, , 2011b. Although the neural mechanisms that underlie these effects of a pre-exposure to vibrotactile stimulation on perception remain to be established with absolute certainty, multiple animal studies have demonstrated that such a preexposure is reliably accompanied by reductions in neuronal responsivity at both peripheral and central levels of the somatosensory nervous system (Tommerdahl et al, 2010a).…”

“…These findings suggest that the method could be viewed as a potential indicator or marker of systemic cortical alterations, as adaptation, at this short duration time scale, is impacted by a number of factors. In particular, these factors include GABA and NMDA receptormediated neurotransmission, and neuron-glial interactions (for discussion, see (Folger et al, 2008;Francisco et al, 2008;Tannan et al, 2007Tannan et al, , 2008Tommerdahl et al, 2007aTommerdahl et al, , 2010aTommerdahl et al, , 2010bZhang et al, 2009Zhang et al, , 2011aZhang et al, , 2011b which play significant roles in the way in which cortical information processing capacities of a number of clinically-identified subject populations are impacted by their respective disorders.…”

“…These tests, from start to finish, lasted approximately twenty minutes and consisted of evaluations of reaction time (RT), vibrotactile threshold, and amplitude discrimination (AD) protocols. The individual tests -all described in previous reports (Folger et al, 2008;Francisco et al, 2008;Tannan et al, 2005Tannan et al, , 2007Tannan et al, , 2008Tommerdahl et al, 2007aTommerdahl et al, , 2007bZhang et al, 2009Zhang et al, , 2011aZhang et al, , 2011b -are described below.…”

Sensory Integration of Apparent Motion Speed and Vibration Magnitude

“…For many sensory modalities, the perception follows Weber's law according to which w = 4IJND I (Weber fraction) is independent on I [13]. It has been shown that the law applies to vibration magnitude [14], [15], frequency [16], [17] and speed of apparent motion [18]. In 1860, Weber's law has been extended by Fechner to explain the relationship between the stimulus intensity and perceived magnitude of a stimulus.…”