Time filter

Source Type

Dawson City, Canada

Gaskin S.,McGill University | Gaskin S.,Dawson College | White N.M.,McGill University
Hippocampus | Year: 2013

The conditioned cue preference paradigm was used to study how rats use extra-maze cues to discriminate between 2 adjacent arms on an 8-arm radial maze, a situation in which most of the same cues can be seen from both arms but only one arm contains food. Since the food-restricted rats eat while passively confined on the food-paired arm no responses are reinforced, so the discrimination is due to Pavlovian stimulus-reward (or outcome) learning. Consistent with other evidence that rats must move around in an environment to acquire a spatial map, we found that learning the adjacent arms CCP (ACCP) required a minimum amount of active exploration of the maze with no reinforcers present prior to passive pairing of the extra-maze cues with the food reinforcer, an instance of latent learning. Temporary inactivation of the hippocampus during the pre-exposure sessions had no effect on ACCP learning, confirming other evidence that the hippocampus is not involved in latent learning. A series of experiments indentified a circuit involving fimbria-fornix and dorsal entorhinal cortex as the neural basis of latent learning in this situation. In contrast, temporary inactivation of the entorhinal cortex or hippocampus during passive training or during testing blocked ACCP learning and expression, respectively, suggesting that these two structures co-operate in using spatial information to learn the location of food on the maze during passive pairing and to express this combined information during testing. In parallel with these processes we found that the amygdala processes information leading to an equal tendency to enter both adjacent arms (even though only one was paired with food) suggesting that the stimulus information available to this structure is not sufficiently precise to discriminate between the ambiguous cues visible from the adjacent arms. Expression of the ACCP in normal rats depends on hippocampus-based learning to avoid the unpaired arm which competes with the amygdala-based tendency to enter that arm. In contrast, there is cooperation between amygdala- and hippocampus-based tendencies to enter the food-paired arm. These independent forms of learning contribute to the rat's ability to discriminate among spatial locations using ambiguous extra-maze cues. © 2013 Wiley Periodicals, Inc. Source

Soare R.J.,Dawson College | Conway S.J.,Open University Milton Keynes | Dohm J.M.,Tokyo Institute of Technology
Icarus | Year: 2014

The Argyre basin and associated rim-materials in the southern hemisphere of Mars are ancient, having been formed by the impact of a large body ~4. Gya. This notwithstanding, the regional landscape continues to be altered by a multiplicity of geological and geomorphological processes.Three landforms, whose close spatial-association is identified in a new geological map of the Argyre region (~290-360°E; ~30-72°S), feature prominently in the list of very Late Amazonian Epoch alterations:. (a)Small-sized (≤~20m in diameter) and unsorted polygons that exhibit metre to sub-metre elevated margins or shoulders, giving them a low-centred appearance; in "wet" permafrost environments on Earth low-centred polygons (LCPs) often are underlain by ice-wedges.(b)Gullies, seemingly formed by "wet" flow(s) and incised by the LCPs.(c)A putative (possibly ice-rich) latitude-dependent mantle (LDM) that underlies the LCPs and spatially-convergent "wet" gullies in all of our observations.These landforms occur from the middle to the high (near-polar) latitudes of the region and overlie geological units of all ages.Hitherto, the presence of the LCPs has been reported only fleetingly in the literature and only in as much as they have been observed on the walls of a few scalloped depressions in mid-Utopia Planitia. By contrast, we report the ubiquitous occurrence of the LCPs in and around the Argyre impact-basin on gully-margins and adjacent slopes as well as on relatively-flat inter-crater terrain.On the basis of three separate but related lines of reasoning we hypothesise that ice wedges could be present beneath LCP margins in our study region. If we are correct then these LCP sites are geomorphological expressions of boundary conditions that were relatively warm and wet in the recent past.First, substantial ice-wedging in permafrost environments on Earth requires the availability of meltwater. If, as some researchers propose, the formation of some "wet" gullies at the martian mid-latitudes is induced by the localised (slope-side and crater-wall) thaw of the underlying LDM at the gully sites themselves, then meltwater also should be available for ice-wedging and the formation of LCPs at these sites. Interestingly, LCPs are observed on gully-channel walls as expected if meltwater is associated with gully formation; however, in some instances the LCPs are also observed on the slope-side terrain that extends for hundreds of metres beyond the channel walls and even above the gully alcoves. This suggests that the distribution of icy terrain affected by thaw could be much more substantial than has been suggested hitherto.Second, LCPs that are identical in shape and scale to the slope-side LCPs are observed on relatively flat inter-crater terrain (also underlain by the LDM) that is distal from the "wet" gullies. By contrast, here, their distribution extends for kilometres. This too could be indicative of meltwater being more extensive in the regional landscape than most workers have thought possible.Third, on Earth the "dryness" or the "wetness" of a permafrost environment determines whether LCP margins are underlain by sand or by ice. When the observed LCPs and major deposits of sand in the study region are plotted on our new map of the Argyre impact-basin, we see that these deposits are rarely proximal. On the other hand, the LDM underlies the LCPs in all instances and, if modified by thaw, seems to be a likelier source of margin fill for the LCPs than sand. © 2014 Elsevier Inc. Source

Neher A.,Dawson College
Medical Humanities | Year: 2011

Robert Knox (1791-1862) is typically remembered as the Edinburgh anatomist to whom the murderers Burke and Hare sold the bodies of their victims. This association brought Knox infamy and damaged his life and career. Before the Burke and Hare scandal, Knox was one of the most famous, original and influential anatomists in Britain. He was also something of a dandy with a sophisticated appreciation of the visual arts. His most significant writings on artistic subjects were his books A Manual of Artistic Anatomy and Great Artists and Great Anatomists: A Biographical and Philosophical Study. Knox's interesting and independently minded opinions on the central artistic questions of his day were taken seriously by his contemporaries. His demotion in the official history of anatomy following his involvement with Burke and Hare, however, also removed him from the history of art theory in 19th century Britain. Knox was such a magnetic and impressive figure, though, that he has to be brought back to his era and his era is not complete without him. This paper discusses how Knox's writings on anatomy and biology shaped his contributions to art theory. It is a first step towards returning Knox, the art theorist, to the cultural life of 19th century Britain. Source

Neher A.,Dawson College
Social History of Medicine | Year: 2015

William Clift (1775-1849) was John Hunter's last assistant and six years after Hunter's death he became the first conservator of the Hunterian Museum of the Royal College of Surgeons of England. It was the conservator's duty to anatomise murderers whohad been sentenced to death and dissection. Clift dutifully fulfilled his role and recorded any medically noteworthy features of the bodies. But he did somethingquite out of the ordinaryandsingularwhenhedrewcarefulandsensitively observed portraits of the freshly executed criminals. The drawings are captivating because of the way in which they occupy a representational space that does not fit within medical illustration, artistic portraiture, socialdocumentary or any other conventional category. This paper explores the characteristics that the sketches have as representations and discusses the reasons that might have been behind their creation. © The Author 2015. Source

Svec M.,Dawson College
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2015

Unitary evolution law describes isolated particle scattering processes in an empty Minkowski spacetime. We put forward a hypothesis that the physical Universe includes a quantum environment that interacts with some particle scattering and decay processes. While the scattering process is governed by the S-matrix dynamics and its conservation laws and unitarity, the interaction with the environment evolves the produced final state ρf(S) to the observed state ρf(O). To be consistent with the Standard Model this new interaction must be a pure dephasing interaction. Governed by a nonunitary evolution law, it modifies the phases of the S-matrix amplitudes and can give rise to mixing of such amplitudes to form observed amplitudes. We present the first test of unitary evolution law in particle scattering. Conservation of P-parity in strong interactions imposes constraints on partial wave helicity and nucleon transversity amplitudes in πN→ππN processes. An independent set of constraints on these amplitudes is imposed by the S-matrix unitary evolution law. The unitary evolution evolves pure initial states into pure final states leading to 9 independent constraints on 16 components of angular intensities in πN→ππN processes. When expressed in terms of parity conserving transversity amplitudes, all 9 constraints are identities provided a single constraint on the transversity amplitudes holds true. The constraint implies that relative phases between transversity amplitudes of the same naturality and transversity must be 0 or ±π. Assuming a self-consistent set of these unitary phases we use the CERN data on spin observables Ru0 and Ry0 to determine a unique solution for the S- and P-wave moduli below 1080 MeV. The data require ρ0(770)-f0(980) mixing in the S-wave but this unitary solution is excluded by data on observables Rx0 within at least 5 standard deviations. All previous amplitude analyses of πN→ππN processes found nonunitary relative phases in an apparent violation of the unitary evolution law. The contrast between the predicted unitary relative phases and the observed nonunitary phases presents unambiguous evidence for the nonunitary evolution of the produced final state and supports the hypothesis of the existence of a quantum environment and its pure dephasing interaction with particle scattering processes. © 2015 American Physical Society. Source

Discover hidden collaborations