Brain Activity during Stereognostic Discrimination Using the Tongue Measured By Functional Near-Infrared Spectroscopy

Abstract

We previously reported our investigation of the stereognostic ability of the tongue to recognize the shape and size of materials in the mouth and its clinical applications. In the present study, we observed brain activity while performing stereognostic discrimination using the tongue; the changes in levels of oxyhemoglobin (oxy-Hb), deoxyhemoglobin (deoxy-Hb), and total hemoglobin (total-Hb) in the frontal cortex area of 37 healthy individuals (18-75 years old) were measured using a functional near-infrared spectrometer with 45 channels. As an experimental task, the stereognostic test piece (TP) was placed on the center of the tongue dorsum, and subjects moved the TP for shape discrimination without letting it touch the teeth or gums. As a control task, subjects did not move the TP placed on the tongue. Stereognostic task-attributed changes in Hb levels were obtained by subtracting the Hb level of the control task from that of the experimental task. During the stereognostic task, oxy-Hb levels increased in the frontal cortex, including the prefrontal area, in most subjects. However, the results also demonstrated large individual variability. When the degree of change in Hb levels during the stereognostic task was mapped, it was found that the changes in the oxy-and total-Hb levels were similar, while the deoxy-Hb level did not change to the same degree. When subjects were divided into three groups, highly-, moderately-and mildlyincreased oxy-Hb levels, there was a significant negative correlation between age and degree of oxy-Hb level increase. The present study suggests stereognosis may be involved in several different information processing pathways, and that aging may also be a factor in the large variability we observed.

Neural Correlates of Oral Stereognosis—An fMRI Study

“…In this study, oral and manual stereognosis both elicit activation in mainly identical cerebral regions. The only other neurophysiological study dealing with neural correlates of oral stereognosis employed near infrared spectroscopy (NIRS, [ 15 ]), where anatomical precision is not provided by the method. Therefore, the neural correlates of isolated oral stereognosis remain unclear.…”

Activation of Prefrontal Cortex in Process of Oral and Finger Shape Discrimination: fNIRS Study

“…One of the few studies on brain activities during oral stereognosis employed functional near-infrared spectroscopy (fNIRS) to report that activities in the prefrontal cortex decreases with age ( Kawagishi et al, 2014 ); however, it is still not clear whether the prefrontal activities during oral stereognosis differ from those during finger stereognosis. Another neuroimaging study by Fujii et al (2011) compared differences in the brain activities between finger and oral stereognosis directly by using functional magnetic resonance imaging (fMRI), which presented the predominant activities in the insular and the visual association cortices during oral stereognosis; however, the results are not conclusive probably because the effects from the differences in the motor task sequences between the oral and finger shape discrimination tasks were not controlled adequately.…”

Direction-Selective Activation in the Prefrontal Cortex through a Visually Guided Tongue Protrusion Task

“…fNIRS in particular is a popular neuroimaging modality today because it enables the real-time visualization of changes in hemoglobin concentration, which represents neuroactivation-dependent changes in local cerebral hemodynamics, and because the equipment necessary for fNIRS measurement including the device itself, is relatively inexpensive. In addition, because the measurement is performed in a sitting position and the device is portable, fNIRS can be performed relatively readily even in individuals with disorders, further facilitating its application in the field of rehabilitation [22][23][24][25].…”