Humean dispositionalism

Humean metaphysics is characterized by a rejection of necessary connections between distinct existences. Dispositionalists claim that there are basic causal powers. The existence of such properties is widely held to be incompatible with the Humean rejection of necessary connections. In this paper I present a novel theory of causal powers that vindicates the dispositionalist claim that causal powers are basic, without embracing brute necessary connections. The key assumptions of the theory are that there are natural types of causal processes, and that manifestations of powers are identified with certain kinds of causal processes. From these assumptions, the modal features of powers are explained in terms of internal relations between powers themselves and the process-types in which powers are manifested.     

Relevant Restricted Quantification

The paper reviews a number of approaches for handling restricted quantification in relevant logic, and proposes a novel one. This proceeds by introducing a novel kind of enthymematic conditional.     

Excitotoxic lesions restricted to the dorsal CA1 field of the hippocampus impair spatial memory and extinction learning in C57BL/6 mice

Recent studies in patients with hippocampal lesions have indicated that the degree of memory impairment is proportional to the extent of damage within the hippocampus. Particularly, patients with damage restricted to the CA1 field demonstrate moderate to severe anterograde amnesia with only slight retrograde amnesia. Comparable results are also seen in other species such as non-human primates and rats; however, the effect of selective damage to CA1 has not yet been characterized in mice. In the present study, we investigated the effects of excitotoxic (NMDA) lesions of dorsal CA1 on several aspects of learning and memory performance in mice. Our data indicate that dorsal CA1 lesioned mice are hyperactive upon exposure to a novel environment, have spatial working memory impairments in the Y-maze spontaneous alternation task, and display deficits in an 8-arm spatial discrimination learning task. Lesioned mice are able to acquire an operant lever-press task but demonstrate extinction learning deficits in this appetitive operant paradigm. Taken together, our results indicate that lesions to dorsal CA1 in mice induce selective learning and memory performance deficits similar to those observed in other species, and extend previous findings indicating that this region of the hippocampus is critically involved in the processing of spatial information and/or the processing of inhibitory responses.     

A secreted form of the beta-amyloid precursor protein (sAPP695) improves spatial recognition memory in OF1 mice

The beta-amyloid precursor protein (APP) plays a central role in Alzheimer's disease (AD) and appears to be a multifunctional protein. Secreted forms of APP (sAPP) have memory-enhancing effects in certain behavioral paradigms. To investigate sAPP's role in spatial memory processes, we adapted a spatial recognition task and evaluated (1) the performance of OF1 mice after massed training (single 15-min acquisition session) and distributed training (three 5-min acquisition sessions), (2) the decline of spatial recognition performance by introducing different delays (5min, 1, 3, and 24h) between the acquisition and retention phases, and (3) the effects of sAPP(695) on spatial recognition memory. In the present study, mice selectively reacted to a change in the spatial configuration of five objects. Indeed, 3min post-acquisition, mice performed similarly in the massed and distributed versions of the task, by re-exploring the two displaced objects only, whereas mice exposed to the same spatial configuration did not. Additionally, all mice did react to a novel object in a subsequent object recognition phase. Mice detected object displacements 5min, 1h, or 3h post-acquisition, but no more at a 24h-delay. Finally, mice treated with sAPP(695) intracerebroventricularly at a dose of 0.5pg/4microL/mouse, 20-min pre-acquisition or 5-min post-acquisition, still reacted to a spatial change in objects position 24h post-acquisition, in marked contrast to NaCl-treated mice. Our data demonstrate that sAPP(695) significantly improves a form of spatial memory, and confirms the hypothesis of an action of this protein on early memory processes.