Medical engineering. A non-invasive and low-cost method of monitoring of brain activity. It allows functional imaging of brain activity through monitoring of blood oxygenation and blood volume in the pre-frontal cortex. Changes in the concentration of oxy-haemoglobin and deoxy-haemoglobin as well as the changes in the redox state of cytochrome-c-oxidase are measured by their different specific spectra in the near-infrared range between 700-1000 nm. This method can be applied to examine how brain activity is affected by certain tasks or behaviors.