Temperature effects on TMS-Derived measures of cortical excitability: a systematic review and implications for a warming climate.

OBJECTIVE

To systematically review evidence on the effects of temperature manipulation on transcranial magnetic stimulation (TMS)-derived measures of cortical excitability in healthy individuals and temperature-sensitive neurological conditions.

METHODS

Following PRISMA guidelines, we searched PubMed, Cochrane Library, EMBASE, and MEDLINE through November-December 2025. Studies reporting quantitative TMS-EMG or TMS-EEG outcomes after experimentally induced, non-noxious temperature changes were included. Parallel searches examined healthy populations and six temperature-sensitive neurological conditions.

RESULTS

Twenty-one studies in healthy individuals (n = 360, mean age 30.9 ± 5.7 years) and one study in multiple sclerosis (MS) met inclusion criteria. Temperature manipulations included whole-body (core changes -2.4 °C to +1.5 °C) and focal interventions (-22 °C to +18 °C). Most studies reported no significant effects on motor evoked potential (MEP) amplitude (73.3%), latency (71.4%), cortical silent period (85.7%), or paired-pulse measures (100%). Effect directions were inconsistent in studies reporting significant findings. The single MS study demonstrated heat-induced impairment, with increased motor threshold and decreased MEP amplitude, not observed in controls.

CONCLUSIONS

Experimental TMS studies largely show null effects of temperature on cortical excitability in healthy individuals, contrasting with epidemiological evidence of temperature-related neurological vulnerability. This discrepancy likely reflects modest brain temperature changes, peripheral confounds, and limited ecological validity of current paradigms.

SIGNIFICANCE: There is a critical need for climate-relevant experimental designs incorporating sustained thermal exposure and direct cortical readouts (e.g., TMS-EEG) in temperature-sensitive populations to elucidate mechanisms of thermal vulnerability.