Most of the Early and mid-Holocene paleoclimate studies in tropical South America indicate a drier climate in Amazon and Southeast Brazil and a wetter climate in Venezuela. This pattern has been interpreted as a northward migration of the Intertropical Convergence Zone (ITCZ) due to insolation changes explained by Milancovitch cycles. We show how model simulations and model-data comparisons can help to investigate further the reason of these changes by considering the mid-Holocene period (6 ka). The insolation effect and the vegetation interaction on the seasonal cycle are explored with emphasis on the regional impact on precipitation and on the atmospheric circulation. A major feature of the mean mid-Holocene simulated climate is indeed the decrease of the rainfall in the South Atlantic Convergence Zone (SACZ) region compared to present day, which is confirmed by the proxy data. However, the ITCZ migrates southward during the Southern Hemisphere summer thus enhancing the precipitation in Northeast Brazil. The SACZ and ITCZ displacements are enhanced by the vegetation feedback. The analysis of the transient meridional heat transport and of the baroclinicity of the model climate suggests more intense winter and early spring cold outbreaks in the central region of South America, which seems in agreement with paleoclimate proxies.