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Adult male rats were implanted with chronically indwelling recording electrodes in the dentate hilus of one hemisphere and bipolar stimulating electrodes in the contralateral entorhinal cortex (EC). Daily measurements were then made of the amplitude of responses, evoked through the crossed temporodentate (CTD) pathway, while the rats were unanesthetized and unrestrained. The implanted rats were also trained to alternate turns in a T-maze, with the use of a rewarded-alternation procedure. After reaching criterion performance in the alternation task, each rat was given a lesion of the EC ipsilateral to the recording electrode (n = 14) or a sham lesion (n = 5). Mean amplitudes of the evoked responses increased over Postlesion Days 4-11, probably due to reactive synaptogenesis in the CTD system, reaching a level that was significantly elevated above prelesion levels by Postlesion Day 6. Rats given EC lesions exhibited a transient impairment in alternation performance, with the mean alternation score significantly below prelesion levels on Postlesion Days 2-6. Although 2 EC-lesioned rats did not show a behavioral deficit, the electrophysiological increases and behavioral recovery were correlated in the remaining 12 cases (Pearson r = .73). These results are consistent with the interpretation that sprouting by the CTD system contributes to recovery of T-maze alternation performance following unilateral EC lesions.

Numerical acoustic radiation prediction schemes have developed to the point where they can be used to reliably predict the acoustic response of a vibrating structure. However, the objective of many of the applications of these techniques is the design of a best structural/acoustic configuration for a given application. Thus, the acoustic radiation prediction scheme must be incorporated into a design methodology. Traditionally, the most difficult design variables to incorporate into numerical prediction schemes have been those which define the geometry of the configuration, normally referred to as shape variables. In this investigation, a technique for computing the design sensitivity of the radiated pressure solution to shape variables is formulated and verified. The method uses a boundary element implementation of the Helmholtz integral equation. The potential problems at the characteristic nonuniqueness frequencies of the Helmholtz integral equation are also addressed. The technique is verified for several pulsating sphere examples where analytical solutions are available.

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