Impact of cognitive function on oral perception in independently living older people

Brain mechanisms of oral multisensory processing related to oral health: a systematic review of neuroimaging findings

AIM

Oral functions related to eating, including mastication, swallowing, and taste, are fundamentally a multisensory experience that relies on the crossmodal interaction of touch, gustation, temperature, pain, and proprioception. The brain mechanisms of oral multisensory processing related to eating have remained unknown.

METHODS

The current systematic review summarizes the findings from neuroimaging studies (mainly functional magnetic resonance imaging) focusing on the interaction of multiple sensory stimuli in human participants. Neuroimaging studies of human adults on the interaction between multiple sensory stimuli related to oral functions were identified and extracted via three electronic databases and reviewed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses.

RESULTS

Thirteen primary studies were eligible to be included in this review. Five studies investigated the interaction of intraoral (i.e., sensorimotor, taste, and noxious) stimuli. Six studies investigated the interaction between intraoral and extraoral (i.e., auditory, olfactory, and visual) stimuli. One study investigated the audio-visual interaction on dental fear, and another study investigated sensorimotor processing of eating tools. The studies showed great diversity in the experimental design of crossmodal interaction. Regarding the brain features related to the interaction, the somatosensory and motor regions were mostly reported in the studies.

CONCLUSIONS

The systematic review revealed a complex pattern of brain activation of oral multisensory processing, which can be attributed to the diversity in the experimental design of crossmodal interaction. The findings highlight the role of multisensory integration in maintaining oral health.

Effects of tongue lesions and palatal coverage on oral sensory functions

STATEMENT OF PROBLEM

Oral stereognosis (OS) plays a significant role in the oral rehabilitation of patients with edentulism, as it influences their adaptation to new prostheses. Because of the essentially tactile characteristic of oral sensory perception, the tongue and palate appear to have a crucial function in OS. However, little is known about the influence of tongue lesions on OS and sensorial function. In addition, controversies remain regarding the role of the palate.

PURPOSE

The purpose of this clinical study was to evaluate whether tongue lesions and palatal coverage are disruptive to OS and gustatory function.

MATERIAL AND METHODS

Seventy participants (mean age=30.7 ±6.7 years) were divided into a tongue lesion group (experimental; n=35) and a control group (n=35). The tongue lesion group included participants with geographic, fissured, or hairy tongue. OS was evaluated with the oral stereognosis ability (OSA) test. Gustatory function was assessed with exposure to flavored solutions. After completing the above tests, the participants received a palate covering device, and then OS and gustatory function were immediately reevaluated. Data were analyzed with the Mann-Whitney and Wilcoxon tests (α=.05).

RESULTS

OSA and gustatory function scores did not differ among the tongue lesion and control groups with and without palatal coverage (all P>.05). After palatal coverage, the tongue lesion group took more time to perform the OSA test than the control group (P<.05).

CONCLUSIONS

Neither the presence of tongue lesions nor palatal coverage influenced OS or gustatory function. The OSA test response times were longer for the tongue lesion group after they had received palatal coverage.

Multidimensional insights about healthy aging from the cohort study for community-dwelling older adults: The SONIC study

The Septuagenarian, Octogenarian, Nonagenarian Investigation with Centenarian (SONIC) study was established considering population trends and targeting the oldest-old population. This study is unique in its narrow age range, consisting of individuals aged in their 70s, 80s and 90s, and is carried out as a longitudinal cohort study with follow ups every 3 years in urban and rural areas of eastern and western Japan. The aims of the SONIC study are primarily to clarify aging-related changes in multiple domains of human functioning, explore the dynamics of interactions among these domains and identify factors influencing healthy longevity, including psychological well-being. Investigations spanning medical, dental, nutritional, psychological and sociological fields were carried out by specialists, yielding important results. Findings from the SONIC study in Japan, a super-aged society, will provide valuable information for addressing the global aging trend. This review introduces the results from the SONIC study, and explains factors contributing to healthy longevity and happy aging. Geriatr Gerontol Int 2025; 25: 346-355.

The Relationship between Removable Dental Prostheses and Brain Activity in Elderly Individuals: Systematic Review

BACKGROUND

There is an increasing body of literature associating edentulism with cognitive impairment. The aim of this systematic review was to summarize the available data, emphasizing the role of removable dental prostheses in preventing cognitive deterioration and promoting brain health in elderly individuals.

AIM

This systematic review investigates the relationship between the use of removable dental prostheses and physiological or adaptive changes at the cerebral level in partially and completely edentulous patients.

METHODS

A systematic review was conducted following PRISMA guidelines, with an initial search across PubMed, Scopus, and Web of Science databases. Studies published up to June 2023 in English were considered. A risk of bias assessment was performed for included studies.

RESULTS

Of the 86 studies initially screened, 13 met the inclusion criteria. Findings indicate a positive association between the use of removable dental prostheses and improved cognitive function, with potential therapeutic implications for managing cognitive decline.

CONCLUSION

Removable dental prostheses play a crucial role in enhancing neurological health and preventing cognitive decline, making them an important consideration in the management of neurodegenerative diseases.

Effects of Long-Chain Polyunsaturated Fatty Acids in Combination with Lutein and Zeaxanthin on Episodic Memory in Healthy Older Adults

Arachidonic acid (ARA), docosahexaenoic acid (DHA), and eicosapentaenoic acid (EPA), which are long-chain polyunsaturated fatty acids (LCPUFAs), as well as lutein (L) and zeaxanthin (Z), can potentially improve brain function. However, the effect of a combination of these components (LCPUFAs + LZ) on memory function in healthy older individuals remains unclear. This study aimed to determine if LCPUFAs + LZ-supplemented food could improve memory function. Exploratory and confirmatory trials (Trials 1 and 2, respectively) were conducted in healthy older Japanese individuals with memory complaints. We conducted randomized, double-blind, placebo-controlled, parallel-group trials. Participants were randomly allocated to two groups: placebo or LCPUFAs + LZ. LCPUFAs + LZ participants were provided with supplements containing ARA, DHA, EPA, L, and Z for 24 weeks in Trial 1 and 12 weeks in Trial 2. Memory functions were evaluated using Cognitrax before and after each trial. Combined analyses were performed for subgroups of participants with cognitive decline in Trials 1 and 2. The results showed that supplementation with LCPUFAs + LZ did not significantly affect memory function in healthy, non-demented, older individuals with memory complaints whereas it improved memory function in healthy, non-demented, older individuals with cognitive decline.

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

Background

The 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).

Methods

Six 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).

Results

No 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.

Conclusion

The 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.