Serotonin is a biologically active amine present in the brain and the peripheral tissue of mammals. Serotonin has a variety of functions depending on the compartment in which it is active. During development, serotonin activity results in the formation of highly organized structures in the somatosensory cortex of rats, called barrel fields. The aim of this graduation thesis was to examine the effect of high serotonin levels during perinatal development on the formation and structure of barrel fields. We used rat brains isolated from 3 different experimental groups of rats, each group corresponding to 3 different treatments: 5-hydroxytryptophan (5HTP, serotonin precursor), tranylcypromine (TCP, serotonin degradation inhibitor) and saline (control group). We made sections of the somatosensory cortex which we stained using the Nissl staining method. Having found barrel fields under the microscope, we scanned and photographed them. After we completed the qualitative analysis, we used the softwere ImageJ to draw barrels which belong to the part of the somatosensory cortex that receives input from the rat's whiskers. We measured the area, perimeter and Feret's diameter. After comparing the mentioned geometric parameters, we concluded that elevated serotonin levels disrupt the pattern of barrel formation and their cytoarchitecture in the somatosensory cortex of rats. When compared with the control group, the 5HTP treatment resulted in barrels having smaller areas while the TCP treatment disrupted their structure.