Animals with one of septal, medial thalamic or tegmental reticular formation lesions were compared on three measures of spontaneous activity (a brief test in a novel maze and seven-day tests in running wheels or photocells cages) and on active avoidance learning. Wheel running was depressed by all the lesions (especially septal and tegmental lesions) while locomotion in the maze and photocell cages was unaffected. Avoidance learning was depressed by septal and thalamic lesions but not by tegmental lesions. These results are discussed in terms of the hypothesis that these brain structures form part of systems which facilitate or inhibit somatomotor activity. / Thesis / Master of Arts (MA)