The Effects of Ketamine on the Brain’s Spontaneous Activity as Measured by Temporal Variability and Scale-Free Properties. A Resting-State fMRI Study in Healthy Adults.

Converging evidence from a variety of fields, including psychiatry, suggests that the temporal correlates of the brain’s resting state could serve as essential markers of a healthy and efficient brain. We use ketamine to induce schizophrenia-like states in 32 healthy individuals to examine the brain’s resting states using fMRI. We found a global reduction in temporal variability quantified by the time series’ standard deviation and an increase in scale-free properties quantified by the Hurst exponent representing the signal self-affinity over time. We also found network-specific and frequency-specific effects of ketamine on these temporal measures. Our results confirm prior studies in aging, sleep, anesthesia, and psychiatry suggesting that increased self-affinity and decreased temporal variability of the brain resting state could indicate a compromised and inefficient brain state. Our results expand our systemic view of the temporal structure of the brain and shed light on promising biomarkers in psychiatry