A recent study published in Scientific Reports investigated the relationship between blood electrolyte levels and cortical excitability in healthy adults. The research indicates that plasma sodium levels, even within the normal physiological range, correlate with individual differences in resting motor threshold (RMT), a measure of brain excitability.
Study Methodology
The analysis was a secondary evaluation of baseline data collected from 42 healthy adults aged 18 to 30 years. Participants' plasma concentrations of sodium, chloride, potassium, calcium, and phosphate were measured. Cortical excitability was assessed using transcranial magnetic stimulation (TMS) to determine the resting motor threshold (RMT). RMT is calculated by stimulating the motor cortex and identifying the minimum intensity required to elicit a muscle response in at least half of the attempts. Lower RMT values suggest greater corticospinal excitability.
Key Findings
- A statistically significant positive correlation was observed between plasma sodium concentration and RMT. This indicates that lower sodium levels were associated with lower motor thresholds, suggesting increased cortical excitability.
- All participants' sodium levels were within the standard clinical reference range of 136 to 143 mmol/L.
- No significant associations with RMT were found for other electrolytes including chloride, potassium, calcium, or phosphate.
- The association between sodium levels and RMT remained consistent after adjusting for age and sex.
Interpretation and Future Research
These findings suggest that minor variations in blood sodium concentration, even when within clinically normal parameters, are associated with differences in resting motor threshold. The authors hypothesize that reduced extracellular sodium may influence membrane electrophysiology by affecting sodium channel dynamics or tissue conductivity, thereby altering the effective magnetic field during TMS stimulation.
The study notes that the data reflect associations rather than causal effects. Further research is recommended, including experimental manipulation of sodium levels, individualized electric field modeling, and longitudinal study designs, to determine if sodium levels directly influence cortical excitability.