Abstract
BackgroundThe differences in the brain activities of the insular and the visual association cortices have been reported between oral and manual stereognosis. However, these results were not conclusive because of the inherent differences in the task performance-related motor sequence conditions. We hypothesized that the involvement of the prefrontal cortex may be different between finger and oral shape discrimination. This study was conducted to clarify temporal changes in prefrontal activities occurring in the processes of oral and finger tactual shape discrimination using prefrontal functional near-infrared spectroscopy (fNIRS).MethodsSix healthy right-handed males [aged 30.8 ± 8.2 years (mean ± SD)] were enrolled. Measurements of prefrontal activities were performed using a 22-channel fNIRS device (ETG-100, Hitachi Medical Co., Chiba, Japan) during experimental blocks that included resting state (REST), nonsense shape discrimination (SHAM), and shape discrimination (SHAPE).ResultsNo significant difference was presented with regard to the number of correct answers during trials between oral and finger SHAPE discrimination. Additionally, a statistical difference for the prefrontal fNIRS activity between oral and finger shape discrimination was noted in CH 1. Finger SHAPE, as compared with SHAM, presented a temporally shifting onset and burst in the prefrontal activities from the frontopolar area (FPA) to the orbitofrontal cortex (OFC). In contrast, oral SHAPE as compared with SHAM was shown to be temporally overlapped in the onset and burst of the prefrontal activities in the dorsolateral prefrontal cortex (DLPFC)/FPA/OFC.ConclusionThe prefrontal activities temporally shifting from the FPA to the OFC during SHAPE as compared with SHAM may suggest the segregated serial prefrontal processing from the manipulation of a target image to the decision making during the process of finger shape discrimination. In contrast, the temporally overlapped prefrontal activities of the DLPFC/FPA/OFC in the oral SHAPE block may suggest the parallel procession of the repetitive involvement of generation, manipulation, and decision making in order to form a reliable representation of target objects.
Highlights
Irving (1968) noted that stereognosis can be defined as the ability to recognize objects using only tactile sensation and that it has been applied to the finger and mouth.The neurophysiological mechanisms for finger stereognosis have been investigated intensively, in which the participation of fronto-parietal networks was observed in the process of haptic shape recognition (Shomstein, 2012; Katsuki and Constantinidis, 2014; Sathian, 2016; Xu et al, 2020)
Grand Averaged Waveforms and Topographical Maps of Prefrontal functional near-infrared spectroscopy (fNIRS) Activities The grand averaged waveforms in the six subjects for changes in [oxy-Hb] and [deoxy-Hb] during the REST, finger shape discrimination with no test pieces (F-SHAM), finger shape discrimination (F-SHAPE), Oral shape discrimination with no test pieces (O-SHAM), and oral shape discrimination (O-SHAPE) blocks are shown on the left side of Figure 2, while the [oxy-Hb] maps for changes in [oxy-Hb] in the pre-task, task, and post-task periods during the REST, F-SHAM, F-SHAPE, O-SHAM, and O-SHAPE blocks are presented on the right side of Figure 2
In the comparison between F-SHAPE and O-SHAPE, the values for [oxy-Hb] for F-SHAPE significantly increased as compared to O-SHAPE at fNIRS channel (CH) 1 which corresponds to the dorsolateral prefrontal cortex (DLPFC)
Summary
Irving (1968) noted that stereognosis can be defined as the ability to recognize objects using only tactile (somatic) sensation and that it has been applied to the finger and mouth.The neurophysiological mechanisms for finger stereognosis have been investigated intensively, in which the participation of fronto-parietal networks was observed in the process of haptic shape recognition (Shomstein, 2012; Katsuki and Constantinidis, 2014; Sathian, 2016; Xu et al, 2020). 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); 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; 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. This study was conducted to clarify temporal changes in prefrontal activities occurring in the processes of oral and finger tactual shape discrimination using prefrontal functional near-infrared spectroscopy (fNIRS)
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