Divide the sushi rice into 4 equal portions. Cut the salmon into strips about 1cm wide. Place a sheet of nori, shiny-side down, on a bamboo mat, or a sheet of parchment paper on a board. Spread a portion of rice over the nori, pressing it down evenly and leaving a 1 cm space at the top an bottom. PLace a quarter of the salmon along the middle of the layer of rice, then spread the salmon with a 1/2 teaspoon of the wasabi paste.