1. Olds, J., and Olds, M. E., in Brain Mechanisms and Learning, edit. by Delafresnaye, J. F. (Blackwell, Oxford, 1961).
2. Miller, N. E., in Electrical Stimulation of the Brain, edit. by Sheer, D. E. (Texas Univ. Press, Austin, 1961).
3. Herberg, L. J., J. Comp. Physiol. Psychol., 56, 679 (1963).
4. Symonds, C., Brain, 82, 10 (1959).
5. Efron, R., Brain, 80, 251 (1957).