Reinterpreting the Frequency Dependence of Cortical Auditory-Evoked Response Amplitudes in Light of Current Understanding of Cortical Tonotopic Organization.

The pooled studies mostly date from an era of few electrodes and little data sharing, so the data contain no scalp maps at all. That matters, because the model's central prediction, that the current tilts forward as frequency rises, is exactly what scalp maps would test. Most studies reported the late-latency response. Only five reported the middle-latency response, and those covered a narrow frequency range, so that component is the weakest part of the analysis. Many older studies did not clearly report how many people contributed to each condition, so the participant numbers behind each averaged amplitude are approximate. The search was semi-systematic. One reviewer screened the records, sources and dates were unrestricted rather than systematic, and no risk-of-bias assessment was carried out. The simulation assumed every stimulus frequency produced the same density of neural current, so any real change in the strength of the neural response with frequency is not captured by the model. The model used one averaged template brain with a single Heschl's gyrus in each hemisphere, so it says nothing about people whose gyrus is duplicated, which is common, and ignores individual differences in auditory cortex shape. The fitted contributions of each area should be read as an illustration only: the model could not separate all three areas at once, and MEG responses were not simulated. The authors call the work a first step.

The research was funded by the UK Medical Research Council (grant numbers G0901321, MC_UU_00010/2, MR/S003320/1) and the NIHR Nottingham Biomedical Research Centre. The funding statement supplied names no commercial sponsor.

Do not read the smaller cortical responses at high frequencies as proof that the auditory cortex responds less. The authors' own simulation says the drop can be mostly a matter of the net current turning away from the recording electrodes while source strength stays much the same, and that prediction could not be tested against the pooled data. This is a modelling paper, not a study of patients.