A differentiation was made between dispositional memory and representational memory. A delayed-nonmatching-to-sample task in a T-maze operationalized this distinction. Experimental brain lesions in posterior septum and in prelimbic cortex resulted in amnesia for representational memories. The amnesia ameliorated as a function of continued reinforced postoperative testing. When lesions were placed in both structures in the same animals, amnesia for representational memories also occurred, and with further testing, the amnesia ameliorated as indicated by group data. However, examination of the behavioral performance and the lesions in individual animals revealed that when both lesions were adequate, choices remained at chance levels, results suggesting permanent amnesia for representational memories. That the lesion-induced amnesia was restricted to representational memory was indicated by the fact that the rats displayed no amnesia for dispositional memories regarding what to do in the maze. They did not act like naive animals, as they should if they had forgotten the dispositional memories necessary for successful T-maze performance.For almost a century (James, 1890), it has been customary for students of memory to divide hypothetical memory processes into two types. Squire (1982) described some of these classificatory divisions and remarked that the nervous system "honors" these distinctions. In the present article we describe some effects of brain lesions on one type of memory.At a simple, empirical level, this article distinguishes between dispositional memory and representational memory. A necessary (and commonly made) presumption is that memory is not a datum but is an inferred concept based on observable and learned discriminative responses, that is, a differential response (choice) between two or more cue stimuli. If the discrimination The authors are indebted to Mary G. Capozzi for assistance in preparing the manuscript and to Jean A. Conlon for assistance with the histological work.
Möbius sequence features masklike facies with sixth and seventh nerve palsy and frequently micrognathia thought to result from a neuromuscular deficiency in early movement of the mandible. Failure to thrive in infancy is commonly due to feeding and aspiration difficulties. We present the first description of prenatal sonographic findings associated with this lesion, which also support an in utero developmental etiology of this rare condition.
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