BDNF and schizophrenia: However, a relationship between circulatingBDNF levels and brain activity during learning has not been demonstrated in humans.Reduced brain BDNF levels are found in schizophrenia and functional neuroimaging studiesof probabilistic association learning in schizophrenia have demonstrated reducedactivity in a neural network that includes the prefrontal and parietal cortices and thecaudate nucleus.