Different intensities of unsignalled inescapable shock treatments as determinants of non-shock-motivated open field behavior: A resolution of disparate results

Five days of a 3 min unsignalled, inescapable shock treatment with intensities of either 1.25 mA (low shock) or 4 mA (high shock) was given to 2 groups of rats. A third group was not shocked. Starting 1 week after shock treatment, all rats were given 3 blocks of consecutive daily test sessions in an open field, each block being separated by several days of rest. Test results indicated that animals in the high-shock group moved and reared less, and defecated more than any of thy others during each of the three test blocks (the differences being most pronounced in Test Block 1). The non-shocked animals were the most active and the least likely to defecate of any on Test Block 1, and were the only animals to show habituation of these measures over test blocks. A transfer-of-acquired-fear hypothesis rather than any of three other current theories of shock treatment effects was supported by these data.