Acute effects of subanesthetic ketamine on cerebrovascular hemodynamics in humans: A TD-fNIRS neuroimaging study

Abstract

Quantifying neural activity in natural conditions (i.e. conditions comparable to the standard clinical patient experience) during the administration of psychedelics may further our scientific understanding of the effects and mechanisms of action. This data may facilitate the discovery of novel biomarkers enabling more personalized treatments and improved patient outcomes. In this single-blind, placebo-controlled study with a non-randomized design, we use time-domain functional near-infrared spectroscopy (TD-fNIRS) to measure acute brain dynamics after intramuscular subanesthetic ketamine (0.75 mg/kg) and placebo (saline) administration in healthy participants (n = 15, 8 females, 7 males, age 32.4 +/- 7.5 years) in a clinical setting. We found that the ketamine administration caused an altered state of consciousness and changes in systemic physiology (e.g. increase in pulse rate and electrodermal activity). Furthermore, ketamine led to a brain-wide reduction in the fractional amplitude of low frequency fluctuations (fALFF), and a decrease in the global brain connectivity of the prefrontal region. Lastly, we provide preliminary evidence that a combination of neural and physiological metrics may serve as predictors of subjective mystical experiences and reductions in depressive symptomatology. Overall, our studies demonstrated the successful application of fNIRS neuroimaging to study the physiological effects of the psychoactive substance ketamine and can be regarded as an important step toward larger scale clinical fNIRS studies that can quantify the impact of psychedelics on the brain in standard clinical settings.

Change in brain asymmetry reflects level of acute alcohol intoxication and impacts on inhibitory control

“…We used Kernel Flow1 TD-fNIRS system (Flow1, Kernel, Culver City, CA, USA) 26,29 to collect distributions of the times of flight of photons (DTOFs) from more than 2000 channels across the head. The system uses two wavelengths (690 nm and 850 nm) and samples at an effective rate of 7.14.…”

“…Raw data, i.e. the photons' distribution of time of flights (DToFs) for two wavelengths (690 and 850nm) underwent standard preprocessing steps that include obtaining DToF moments (sum, mean, and variance) and converting their variations into relative concentrations of oxygenated hemoglobin (HbO) and deoxygenated hemoglobin (HbR), as described previously 26,29 (Methods).…”

“…To convert the preprocessed DToF moments data to relative changes in oxy-and deoxy-hemoglobin concentrations (HbO and HbR, respectively), we used a sensitivity method described in detail previously 29,[53][54][55] to obtain absorption coefficients at each wavelength. Finally, these coefficients were converted to relative changes in the two chromophores using the extinction coefficients for the two wavelengths and the modified Beer-Lambert law (mBLL) 56 .…”

“…We used Kernel Flow1 TD-fNIRS system (Flow1, Kernel, Culver City, CA, USA) 26,29 to collect distributions of the times of flight of photons (DTOFs) from more than 2000 channels across the head.…”

Time-Domain Diffuse Optical Tomography for Precision Neuroscience

“…The data preprocessing procedures have been extensively detailed in our previous studies ( 15 ) . Initially, we applied a channel selection method based on histogram shape criteria ( 14 ) .…”