Should it matter when we record? Time of year and time of day as factors influencing frontal EEG asymmetry

Resting frontal encephalographic (EEG) asymmetry, often conceptualized as a trait marker for depression, is influenced by occasion-specific factors, including time of year and the time of day of the recording session as demonstrated recently (Peterson and Harmon-Jones, 2009). The current study examined the influence of seasonal and chronological variables on resting frontal asymmetry, and also assessed whether different reference montages or surface transformations were equally susceptible to these influences. In a direct replication attempt, contrary to previous findings, no simple time of year by time of day interaction was found. Time awake at recording, however, was an important moderating variable of the relationship between photoperiod and time of day. EEG asymmetry scores based on current-source density (CSD) transformed data, however, appeared less vulnerable to these influences, providing further evidence to suggest that the CSD transform may be advantageous for examining stable trait estimates of frontal EEG asymmetry.

► Seasonal and chronolobiological influences on resting frontal asymmetry were examined.
► Time awake, photoperiod, and time of day interacted to affect frontal asymmetry.
► Current source density (CSD) transformed data were not vulnerable to these influences.
► CSD transformed data may provide a better trait estimate of resting frontal asymmetry.