Experimental results for the sequential transport through a lateral quantum dot in a perpendicular magnetic field are compared with theory. Regular patterns of negative differential conductances are observed in the nonlinear regime. We attempt to reproduce theoretically these patterns in a simplified model which captures the essential features of the experimental system. Orbital and spin effects are treated in terms of the Fock-Darwin model. The transport properties are described by employing a master equation with tunable tunnelling and relaxation rates. We show that the essential physics underlying the experiment can be described within our approach if the timescales of the different transport channels are well separated.