Substituted pyrazolopyrimidine derivatives of formula (I) wherein Y1, Y2, Y3, Y4 represent N or C—, whereby at least two of the groups Y1 to Y4 represent a carbon atom, R1 represents chloro or bromo, R2 to R7 represent e.g. hydrogen, methyl or ethyl; and R10 and R11 independently represent e.g. hydrogen or C1-C6alkyl, are potent mGluR5 modulators and are useful for the prevention of acute and chronic neurological disorders.