Abstract: The bioassay process for the determination of alterations in neuronal connectivity and/or morphology comprises the operations of:—identifying the critical distance corresponding to which a pair of spaced single neuronal cells, subjected to the assay, is still able to form reciprocally interconnecting neuritic extensions, after a predetermined incubation period under conditions which favour the formation of such neuritic extensions, wherein each of said single neuronal cells is adhered to a respective spot of a substance promoting the adhesion of said neuronal cells, said spots being deposited at a distance from one another onto a substrate inhibiting the adhesion of neuronal cells, and—comparing the critical distance identified with the critical distance determined, under the same conditions, for reference cells, wherein a decrease in said critical distance for the neuronal cells subjected to the assay, relative to the critical distance for the reference cells, is indicative of an alteration in the neuronal c