Effects of foot reflexology on an infant with SNHL: An fMRI case study

doi:10.21203/rs.3.rs-2710677/v1

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Effects of foot reflexology on an infant with SNHL: An fMRI case study

https://doi.org/10.21203/rs.3.rs-2710677/v1

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Foot reflexology is a traditional medicine in which foot stimulation is believed to have therapeutic effects on patients with sensorineural hearing loss (SNHL). However, no physiological evidence of these benefits is available. In the present study, functional magnetic resonance imaging (fMRI) was employed to assess the effects of foot reflexology. Compared with SNHL infants who did not undergo foot reflexology, an SNHL infant treated with foot reflexology exhibited increased regional homogeneity (ReHo) in the frontal cortex, temporal cortex, occipital cortex, and thalamus and decreased ReHo inthe bilateral occipital cortex. This suggests that foot reflexology influences hubs of the brain networks responsible for language and auditory processing. Differences in these areas have clinical significance and may be helpful for treating infants with SNHL.A large-scale, randomized controlled trial is needed to confirm these findings.

Developmental Neuroscience

Cognitive Neuroscience

infants

sensorineural hearing loss (SNHL)

reflexology

Previous studies have established the benefits of reflexology for many diseases, such as relieving anxiety in CABS patients [1], alleviating pain after chest tube removal[2] and improving auditory processing[3]. However, the physiological mechanism of foot reflexology is unclear. In the present study, we aimed to investigate the neural substrates of foot reflexology in infants with sensorineural hearing loss (SNHL).Specifically, alterations in the interregional connectivity of auditory and language areas induced by foot reflexology were detected by covariance analysis of resting-state fMRI data.

Recently, the links between foot reflex areas and brain areas have attracted attention [4–6]. Nakamaru et al.(2008) found that reflexological stimulation of the foot reflex areas corresponding to the eye, shoulder,and small intestine can activate the corresponding somatosensory areas. This study scientifically demonstrated that foot reflex stimulation can lead to neural differences. Another study compared the neurophysiological effects ofSwedish massage, reflexology and massage with an object using functional magnetic resonance imaging (fMRI) [5].They reported that activation of the retrosplenial/posterior cingulate after foot reflexology was different from that after Swedish massage and massage with an object. This suggests that foot reflexology has different underlying effects than other kinds of massage. A recent study by Wattanaruangkowit et al.[6] examined the effects of foot reflexology on smoking cessation by fMRI. They found changes in brain areas correlated with foot stimulation, especially in the precentral gyrus of the frontal lobe and the postcentralgyrus of the parietal lobe.They also found that fMRI responses from parts of the frontal and parietal lobes, the temporal and occipital cortices, and the thalamus were not consistent. These different responses had clinical significance and contributed to smoking cessation.

The imaging studies described above on links between brain areas and foot reflex areas were based on task-state analysis. However, this method may detect only a subset of specific neurons, underestimating the size and number of areas involved in task performance [7]. In other words, the effects of foot reflexology may be underestimated. In the present study, we employed resting-state MRI and performed covariance analysis. During the resting state, neurons exhibit spontaneous firing. Such spontaneous firing is always followed by regional cerebral blood flow increases [8]. Neural firing in a specific brain area influences neurons in other brain areas through efferent output. By calculating the covariance of each voxel according to the time course of a selected brain region, it is possible to detect the neurons connected to the selected region [9]. If foot reflexology is beneficial for infants with SNHL, we hypothesize that the brain networks associated with language and the auditory system will exhibit different responses in treated and control infants.

Language processing is supported by different brain areas. The languagenetwork involves two pathways: the dorsal pathway and ventral pathway [10]. The two pathways have different hubs, such as the frontal cortex, temporal cortex and occipital cortex. If foot stimulation has therapeutic effects on patients with sensorineural hearing loss (SNHL), we hypothesise that activation of brain areas in the infant will different from those in infants not treated with foot reflexology.

The case in this case study was a 3-month-old girl with SNHL. She did not pass a new-born hearing screening examination according to her parents’ oral report. At the age of three months, her parents took her to a hearing screening centre at the hospital affiliated with North Sichuan Medical College (NSMC) for a confirmatory test with ABR. The patient’s parents were informed of the purpose of the study and the process. Informed written consent was provided by the parents of the infant in line with the ethical principles of the NSMC. In addition, 6 infants with SNHL were recruited as a control group and did not receive foot reflexology.

Before foot reflexology was administered, the infant’s hearing was measured with auditory brainstem response (ABR) to collect a baseline measurement. Her left ear had a threshold of 40 dB, and her right ear had a threshold of 50 dB. After 3 months of foot reflexology, her auditory thresholds decreased (to 30 dB and 40 dB, respectively). After another 3 months of foot stimulation, the auditory thresholds of both ears were below 30 dB. The normal auditory threshold is below 30 dB.

Foot reflexology theory is based on the idea that all body structures are interlinked with specific reflex points on the hands and feet [11].According tofoot reflexology, the auditory cortex is linked with the hallux. Thus, the girl received 30 minutes of foot stimulation each week day, with pressure applied to the left and right halluces by the same reflexologist. The girl underwent 24 weeks of foot stimulation in total.

Before foot reflexology, the girl underwent resting-state fMRI at baseline (T0). After 6 months of stimulation, the girl underwent a third rs-fMRI assessment (T1). The control group also underwent fMRI at the age of 9 months (sd ± 2). All imaging data were acquired on a 32-channel 3.0 T GE MR750 Discovery device while the infants were sedated. Foam padding was used to reduce the loud scanner noise. After structural images were obtained, functional images were acquired with an echo-planar imaging (EPI) sequence. The sequence parameters were as follows: 30 contiguous slices with a slice thickness of 4 mm, repetition time (TR) = 2,000 ms, echo time (TE) = 30 ms, flip angle (FA) = 90°, field of view (FOV) = 24 ×24 cm², data matrix = 64 × 64, and total volumes = 200.

Three radiologists at NSMC were invited to assess the conventional MRI data. After a quality inspection of the raw functional images, SPM12 was employed to perform pre-processing, including slice timing, realignment, and normalization.

Using REST (http://resting-fmri.sourceforge.net), we performed ReHo analysis. The linear trend of the time series was removed, and a band pass filter (0.01 Hz < f < 0.08 Hz) was applied to reducethe influence of physiological noise, such as the respiratory and cardiac rhythms. In this data-driven analysis, the individual ReHo maps of the infant who underwent foot reflexology and those of the 6 infants who did not undergo foot reflexology were generated by assigning each voxel a value corresponding to the KCC of its time series with its nearest 26 neighbouring voxels [12]. The mean ReHo maps of the controls were calculated by DPABI (Yang et al., 2016).By comparing the ReHo map of the treated infant with the mean ReHo map of the control group, we obtained the difference in activation of brain areas using the following formula: mean_{treated infant}– mean_{control group}/SD_{control group}(see Fig. 1 for details).The difference between the treated infant and control groups was attributed to the effects of foot reflexology.

Activation

As shown in Fig. 1, the ReHo values of the bilateral middle temporal cortex, the left frontal lobe, the right thalamus, the right Rolandic operculum and the right caudate were increased after foot reflexology.

Deactivation

As shown in Fig. 2, ReHo of the bilateral middle occipital cortices were decreased after foot reflexology.

This study aimed to assess the effects of foot reflexology on an infant with SNHL using resting-state fMRI (rs-fMRI). rs-fMRI is safe and reliable for predicting cognitive phenotypes and measuring foot reflexology responses ([14],[6]). Compared with the control group, the treated infant exhibited increased ReHo values of the bilateral middle temporal cortex, the left frontal cortex, the right thalamus and the right caudate.

The middletemporal cortex is a major hub of the language network [10]. A neural plasticity study of cochlear implant (CI) users reported that the middle temporal cortex is related to speech performance. In CI users, reduced activation of auditory areas is related to poor speech recovery ([15]; [16]).Studies in healthy individuals have revealed that the MTG participates in mapping phonemes and syllables [15]; [16]). Applying these results to the present study, increased ReHo indicates improvement in mapping phonemes and syllables in the treated infant. This improvement can be attributed to foot reflexology.

The left frontal cortex participates in language processing. Previous studies have revealed that increased activity of the left front cortex is related to speech intelligibility and complex phoneme analysis [17]; [18]. Single words and speech increased activity in the left frontal cortex in the high-comprehension group of CI users. In contrast, low-comprehension CI users exhibited no activity of the frontal cortex. Additionally, Papathanassiou et al. [19] reported that when participants perform passive storylistening, activation of the left temporal lobe includes the inferior part of the prefrontal cortex. Thus, the temporal cortex and left frontal cortex are part of the language circuitry. In the present study, the ReHo of the left frontal cortex was increased in the case compared to the controls. The discrepancy between the case and control groups is attributed to the effects of foot reflexology.

Regarding the thalamus, a guinea pig study revealed that the thalamus participates in sound discrimination[20]. A meta-analysis of overt speech production revealed that the activation of the thalamus is consistent with the activation of the left inferior frontal gyrus (IFG), superior temporal gyrus (STG) (auditory cortex) and other brain areas[21].Thus, at a gross neuroanatomical level, the thalamus is a hub of speech production. In the present study, the increased ReHo of the right thalamus after foot reflexology may indicate an improvement in speech production.

The caudate is a part of the corticostriatal network, which includes the dorsolateral prefrontal cortex, inferior parietal lobule, middle temporal gyrus, caudate, putamen, and ventral striatum[22].This brain network is responsible for learning speech categories. A recent study on the effects of voice treatment for idiopathic PD (IPD) showed neural changes induced by voice treatment, including greater activation of the right caudate compared to that of the control group [23]. This suggests that the right caudate plays a role in coordinating motor patterns involved in speech. In the present study, the increased ReHo of the right caudate may indicate facilitated learning of speech categories.

However, in the present study, we also found decreased ReHo of the bilateral occipital middle cortex compared to that of the control group. The role of the occipital cortex in speech recovery in CI users has been explored ([24]; [25]; [26];[27]).A recent study by Han et al.(2019) reported that glucose metabolism in deaf patients was higher than that in controls. They also found a negative correlation between metabolic activity in the occipital cortex and speech perception outcomes. This suggests that decreased glucose metabolism in this region reflects promotion of speech recovery. Other studies have also demonstrated that activation of the occipital cortex is related to poor speech performance [28],[24]. In the present study, the decreased ReHo of the bilateral occipital cortex may indicate improved speech perception of the treated infant after foot reflexology.

This study demonstrated that foot reflexology benefits infants with SNHL. The activation of auditory areas and hubs of the language network, such as the middle temporal gyrus, thalamus, and frontal cortex, was enhanced by foot reflexology. In contrast, the activation of the occipital cortex was decreased. To the best of our knowledge, this is the first study to report physiological evidence that foot reflexology affects infants with SNHL.

This study has the following limitations. First, the sample size was small. Although a larger group sizes may be difficult to recruit, such studies would be beneficial. In particular, a prospective randomized controlled trial comparing foot reflexology and sham treatment for infants with SNHL is recommended. Second, the hearing loss of the control group was not matched to that of the treated infant, potentially inducing bias. In future studies, the hearing loss level of the control group should strictly match that of the experimental group.

written consent was received from participants to publish the findings of the research.

Funding

This work was supported by the National Social Science Foundation [grant number 18BYY091, 2018]

Disclosure statement

There was no conflict interest

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Effects of foot reflexology on an infant with SNHL: An fMRI case study

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