Objective: To demonstrate the absence of any significant difference in weekly TDT values during two consecutive menstrual cycles in healthy female volunteers.

Background: Temporal discrimination threshold (TDT) detects the point at which an individual determines two stimuli to be asynchronous (normal = 30 – 50 ms). Women, aged 20-40 years, have faster temporal discrimination than men. A recent study demonstrated that 20-year-old women were approximately 13 ms faster than age-matched men – representing a 20% advantage. Mean TDT scores in women increased (worsened) with age when compared with men. Above the age of 40 years women had longer mean TDTs than their male peers. We believe that an abnormal TDT is due to a disorder of the midbrain network for covert attentional orientating. This is caused by reduced gamma-aminobutyric acid (GABA) inhibition. The overall hypothesis is that the sexual dimorphic differences observed in TDT above the age of 40 results from age- and sex-chromosome-related alterations in GABA levels and are not due to hormonal influences.

Methods: Fifteen healthy female volunteers (not taking hormonal contraception) were recruited to the study. Visual TDTs were recorded from participants using portable goggles. Testing was performed weekly, over 9 consecutive weeks. The first week of recording was discarded to allow for practice effect. Participants were asked to keep menstrual diaries for the duration of the study.

Results: Fourteen female participants completed the study. The mean age of participants was 21.9 years (SD 0.989 years). Menstrual cycle length varied between participants (mean 31 days, SD 6.71 days). Menstrual cycle stage was expressed as a quartile of an individual’s total cycle length. The relationship between menstrual cycle stage and the weekly TDT score was assessed using Kruskall Wallis tests. This demonstrated that there was no statistically significant difference in mean TDT scores across the menstrual cycle stages of testing (chi-square 0.650, df 3, p < 0.885).

Conclusions: Our study demonstrates an absence of any significant difference in weekly TDT values during two consecutive menstrual cycles in healthy female volunteers. This supports the hypothesis that sexually dimorphic differences observed in TDT above the age of 40 result from age- and sex chromosome-related alterations in GABA levels and are not due to hormonal influences.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/temporal-discrimination-threshold-and-the-menstrual-cycle/