The hypothesis that memories are stored as a specific distribution of strengths in a population of modifiable synapses was examined by the bilateral induction of long-term enhancement in synapses of the main afferent fiber system to the hippocampal formation in rats. Brief, high-frequency activation of the perforant pathway in chronically prepared animals resulted in a persistent increase in the field EPSP and population spike, measured extracellularly in fascia dentata. This treatment resulted in a profound and persistent deficit in the acquisition of new spatial information in a task requiring spatial "reference" memory, and disruption of recently acquired spatial information. Well-established spatial memory was completely unaffected, however, as was the acquisition of spatial information into shortterm "working" memory. These results support the hypothesis that, during the formation of "cognitive maps," spatial information must be temporarily stored at modifiable synapses at the input stage to the hippocampal formation, but that this information is not needed once the representation of the environment is well established. Spatial working memory, in a familiar environment, appears not to depend on the distribution of synaptic strengths in this system at all.Most attempts to explain associative learning in the nervous system have invoked long-term changes in the efficacy of cellto-cell communication as the underlying information-storage medium (e.g., Hebb, 1949; Marr, 197 1). The common element of these theories is the assumption that information is stored as a specific distribution of modifiable synaptic weighting functions. These hypotheses predict that a treatment that disrupts such a distribution, by driving the population of modifiable synapses to the maximum strength, will disrupt the information content. This would have two consequences: impaired performance of tasks requiring the integrity of previously stored information, and impaired acquisition of new information. The present experiments were designed to examine this prediction by studying the effects on spatial learning and memory of artificially induced enhancement of synaptic efficacy in a large population of hippocampal synapses.Bliss, Lomo, and Gardner-Medwin first documented that brief episodes of electrical stimulation of perforant path fibers at physiological frequencies resulted in a lasting increase in synaptic transmission to hippocampal target neurons (Bliss and GardnerMedwin, 1973;Bliss and Lomo, 1973). Since this discovery, considerable evidence has accumulated in support of the hypothesis that this experimentally induced phenomenon represents the activation of a physiological process that normally Received Apr. 5, 1985; revised July 15, 1985; accepted July 17, 1985. This work was supported by PHS Grants AGO3376 and NS20331. We thank Seth Sharpless for help with computer software, B. Peterson for secretarial assistance, and P. Sharp and B. Jones Leonard for helpful comments on the manuscript. Lomo (1966) and the term LTP (long-term p...

A completely between-subjects design was used to test three specific hypotheses of hippocampal function: O'Keefe and Nadel's cognitive mapping theory, Olton's workin~-memory ~heory, and Rawlins's temporal discontiguity hypothesis. The performance of rats wlth entorhmallesions was compared with that of controls on a variety of spatial and nonspatial reference-and working-memory tasks using the same apparatus. The effects of massed versus distributed trials were also investigated. The entorhinal-Iesioned animals were impaired on all tests of allocentric localization, regardless of the type of memory tested. The results were en~irely consistent with the predictions of cognitive mapping theory, and failed to support the workmg-memory and temporal discontiguity theories. The results do not rule out the possibility that the cognitive mapping theory might, nevertheless, be a specific case of other, more general theories.During the past decade, two major conflicting behavioral theories have predominated in the animalliterature surrounding hippocampal function: the cognitive rnapping (CM) theory ofO' Keefe and Nadel (l978, 1979) and the working-memory (WM) theory (Honig, 1978) as articulated by Olton, Becker, and Handelmann (l979). In 1985, Rawlins introduced the temporal discontiguity (TD) hypothesis, which shares many of the predictions of WM theory but is in direct conflict with CM theory.CM theory proposes that the hippocampus is the neural substrate for a memory system based on an allocentric spatial framework (or locale system). According to this theory, information about objects, places in the environment, and the relationships among objects and their locations is stored in this system. Thus, the cognitive map would permit an animal to respond flexibly to complex spatial problems. Egocentric response systems (or taxon systems) are ascribed to other parts of the brain. Thus, CM theory predicts that hippocampal damage would disrupt allocentric (place) tasks and would produce no impairment on nonspatial, or egocentric, tasks. WM theory proposes that the hippocampus is the substrate for a memory system that "emphasizes the temporal/personal context that separates one instance from another" (Olton, 1983, p. 338). The WM component of a task is trialspecijic. The temporal span of the memory may be brief or extended and the content of WM may be spatial or nonspatial. Reference memory (RM)This work was included in a dissertation submitted in partial fulfillment ofthe requirements for the PhD degree (to M.R.

Supported catalysts containing an oxophilic metal such as Mo and a noble metal such as Pt have shown promising activity and selectivity for deoxygenation of biomass-derived compounds. Here, we report that PtMo catalysts also promote hydrogenolysis of the model compound benzyl alcohol, while decarbonylation is most prevalent over unmodified Pt. A combination of single crystal surface science studies, density functional theory (DFT) calculations, and vapor phase upgrading experiments using supported catalysts was carried out to better understand the mechanism by which Mo promotes deoxygenation. Molybdenum was deposited in submonolayer quantities on a Pt(111) surface and reduced at high temperature. Temperature-programmed desorption (TPD) experiments using benzyl alcohol as a reactant showed greatly enhanced yields of the deoxygenation product toluene at moderate Mo coverages. To understand how the interaction of the aromatic group with the surface influenced this reactivity, we investigated the adsorption of toluene as a probe molecule. We found that the addition of Mo to Pt­(111) resulted in a significant decrease in toluene decomposition. DFT calculations indicated that this decrease was consistent with decreased aromatic adsorption strengths that accompany incorporation of Mo into the Pt subsurface. The weaker aromatic–surface interaction on Pt/Mo surfaces led to a tilted adsorption geometry for benzyl alcohol, which presumably promotes hydrogenolysis to produce toluene instead of decarbonylation to produce benzene and CO. Alumina-supported Pt and PtMo catalysts were also tested for benzyl alcohol deoxygenation. PtMo catalysts had a higher rate of toluene production and lower rates of benzene and benzaldehyde production. Additionally, when benzaldehyde was used as the reactant to measure decarbonylation activity the mass-normalized rate of benzene production was 2.5 times higher on Pt than PtMo. Overall, the results of TPD, DFT, and supported catalyst experiments suggest that subsurface Mo sites weaken the binding of aromatic rings on PtMo surfaces; the weakened aromatic–surface interaction is correlated with an improvement in selectivity to C–O bond scission.

Understanding surface reactions of biomass-derived oxygenates on metal oxides is important for designing catalysts for valorization of biomass. This work elucidated the effect of different pretreatments on molybdenum trioxide (MoO3) to understand how surface reactivity is controlled by the surface oxidation state. The catalyst was pretreated in oxidative, inert, and reducing environments. The inert and reducing pretreatments created oxygen vacancies on the catalyst surface that acted as active sites for the adsorption of oxygenated molecules, with the reducing pretreatment yielding a higher density of these active sites. Exposing the catalyst to an alcoholic solvent such as methanol also led to a partial reduction similar to the inert pretreatment. After pretreatment, the catalyst was exposed to ethanol, acetaldehyde, and crotonaldehyde with subsequent characterization by diffuse reflectance infrared spectroscopy (DRIFTS), temperature-programmed desorption (TPD), X-ray absorption near edge spectroscopy (XANES), and X-ray photoelectron spectroscopy (XPS). Density functional theory (DFT) was also used to determine adsorption configurations and energies of ethanol, acetaldehyde, and crotonaldehyde. Reduced surfaces were shown to have a stronger affinity for carbonyls, leading to a higher activity for the aldol condensation of acetaldehyde and ethanol to C4 molecules. Catalysts pretreated in an oxidative environment were completely inactive toward chemisorption and reaction of acetaldehyde.

Addition of tungsten to supported platinum catalysts increased the rate of benzyl alcohol hydrodeoxygenation via a bifunctional mechanism, whereas undesirable decarbonylation was suppressed due to blocking of platinum terrace sites.