Exploring the quantum brain with MRI entanglement witnesses Speculations about quantum operations in consciousness and cognition have a long history. Here, I will explore the idea that an unknown quantum operator in the brain could mediate entanglement to known quantum systems, like the proton spins measured with MRI. This indirect approach has the advantage that it can circumvent the problem to measure unknown quantum systems. This measurement problem is probably the foremost reason why quantum effects of the brain haven't been found before. Further, I will discuss how entanglement may influence the MRI signal, and under which circumstances it can be clearly differentiated from non-entangled signals. Finally, I will investigate if the brain may also “disentangle”.