Early and Middle Wisconsinan Environments of Eastern Beringia: Stratigraphic and Paleoecological Implications of the Old Crow Tephra

The widespread Beringian Old Crow tephra occurs in Imuruk Lake (Alaska) core V, above the Blake paleomagnetic event and below Radiocarbon dates, which provide an extrapolated tephra age between 87 000 - 105 000 BP. Exposure KY-11 (Alaska), where the tephra occurs in a dated lacustrine sequence, provides corroboration. Fossil pollen records show that O.C.T. was deposited across northern Beringia on birch-shrub tundra vegetation during an interval of colder climate. A series of climatic oscillations followed tephra deposition. A prolonged period of cold-arid climate ( = marine isotope Stage 4) preceded an interval of warmer than present climate starting ca. 60 000 BP (beginning Stage 3). During this interval, designated the Koy-Yukon thermal event, an exposed Bering land bridge promoted an interglacial type climate that led to significant biotic changes and permafrost degradation. O.C.T. occurs on drift of the Mirror Creek Glaciation which is equivalent to other presumed Early Wisconsinan glaciations in Alaska and Yukon. These glaciations could not have occurred later than marine Stage 5. Stage 4 was fully as cold as Stage 2 (Late Wisconsinan), yet seems not to have been a time of extensive glaciation. The Middle Wisconsinan, 30 000 to more than 80 000 BP, was a nonglacial interval with several climate fluctuations, one of which, the Koy-Yukon thermal event, was warmer than at present.Le tephra de Old Crow, se manifeste, entre autres, au trou de forage V à Imuruk Lake, en Alaska. Puisqu'il se situe après l'inversion magnétique de Blake, mais au-delà de la portée des datations au radio-carbone, la date approximative de son dépôt doit se situer entre 87 000 et 105 000 BP. La coupe KY-11 (Alaska), où l'on trouve le tephra dans une séquence lacustre, appuie cette hypothèse. Les registres de pollen fossile démontrent que le tephra de Old Crow s'est déposé dans le nord de la Béringie dans un milieu de toundra arbustive à bouleau, au cours d'une période froide. Plusieurs oscillations climatiques se sont succédé par la suite. Une longue période de climat aride froid (phase isotopique océanique 4) a précédé un épisode au climat plus chaud que maintenant et qui a commencé vers 60 000 BP environ. Durant cet épisode (que l'on nomme ici Koy-Yukon), l'émergence du pont terrestre de Bering a contribué à l'avènement d'un climat de type interglaciaire, qui a provoqué des changements de type biotique importants et la dégradation du pergélisol. Le tephra de Old Crow surmonte des dépôts de la glaciation de Mirror Creek, qui correspond aux glaciations qui se sont produites en Alaska et au Yukon au cours du Wisconsinien inférieur. Ces glaciations n'ont pu avoir lieu après la phase isotopique 5. Pendant la phase 4, le climat était aussi froid que durant la phase 2 (Wisconsinien supérieur), mais il semble que cette période n'ait connu qu'un englacement limité. Il n'y a pas eu déglaciation pendant le Wisconsinien moyen (de 30 000 à plus de 80 000 BP), mais les fluctuations climatiques ont été nombreuses, dont l'épisode de Koy-Yukon.Das weitverbreitete Tephra von Old Crow, Beringia, findet man auch am Bohrioch V von Imuruk Lake (Alaska). Da es nach der Inversion von Blake und vor Radiokarbondatierungen liegt, mufi die annâhernde Zeit der Tephra-Ablagerung zwischen 87 000 -105 000 v.u.Z. Iiegen. Der Schnitt KY-11 (Alaska), wo das Tephra in einer datierten Seesediment-Folge vorkommt, bestâtigt diese Datierung. Belege von fossilem Pollen zeigen, daf3 Old Crow Tephra in Nord-Beringia in einem Milieu von Birken-Busch-Tundra wâhrend einer Période kàlteren Klimas abgelagert wurde. Auf die Tephra-Ablagerung folgte eine Série von Klima-Schwankungen. Eine lângere Période von kalttrockenem KIima ( = marine isotopische Phase 4) ging einer Phase, die warmer als das heutige Klima war und die etwa 60 000 v.u.Z. begann (Beginn der Phase 3) voraus. Wâhrend dieser Zeitphase. die das thermische Koy-Yukon genannt wird, bewirkte eine ausgesetzte Bering Land-Brucke ein Klima des interglazialen Typus, welches zu bedeutenden biotischen Verànderungen und Permafrost Abtragungen fuhrte. Old Crow Tephra findet sich uber den Ablagerungen der Mirror Creek Vereisung, welche anderen mutmaGlich frùhen Wisconsin Vereisungen in Alaska und Yukon entspricht. Diese Vereisungen kônnen nicht spâter als in der marinen Phase 5 stattgefunden haben. Die Phase 4 war so kalt wie die Phase 2 (spates Wisconsin), scheint jedoch keine Zeit extensiver Vereisung gewesen zu sein. Das mittlere Wisconsin, von 30 000 bis mehr als 80 000 v.u.Z., war eine nicht glaziale Zeitspanne mit gewissen Klima-Schwankungen, deren eine, das thermische Koy-Yukon. warmer als die Jetztzeit war

Acute Alcohol and Cognition: Remembering What It Causes Us to Forget

Addiction has been conceptualized as a specific form of memory that appropriates typically adaptive neural mechanisms of learning to produce the progressive spiral of drug-seeking and drug-taking behavior, perpetuating the path to addiction through aberrant processes of drug-related learning and memory. From that perspective, to understand the development of alcohol use disorders it is critical to identify how a single exposure to alcohol enters into or alters the processes of learning and memory, so that involvement of and changes in neuroplasticity processes responsible for learning and memory can be identified early on. This review characterizes the effects produced by acute alcohol intoxication as a function of brain region and memory neurocircuitry. In general, exposure to ethanol doses that produce intoxicating effects causes consistent impairments in learning and memory processes mediated by specific brain circuitry, whereas lower doses either have no effect or produce a facilitation of memory under certain task conditions. Therefore, acute ethanol does not produce a global impairment of learning and memory, and can actually facilitate particular types of memory, perhaps particular types of memory that facilitate the development of excessive alcohol use. In addition, the effects on cognition are dependent on brain region, task demands, dose received, pharmacokinetics, and tolerance. Additionally, we explore the underlying alterations in neurophysiology produced by acute alcohol exposure that help to explain these changes in cognition and highlight future directions for research. Through understanding the impact acute alcohol intoxication has on cognition, the preliminary changes potentially causing a problematic addiction memory can better be identified

Overview of optical BCI research at NUI Maynooth

A brain-computer interface (BCI) is a device that provides a user with an alternative means of interactive communication, rather than the usual modes via physical gestures/speech. Thus it acts as a neural prosthesis bypassing the normal output pathways of the brain, i.e. spinal cord and periphery cascade. An optical BCI uses optical means of determining the user's mental intent, e.g. to turn on a light switch, by spectroscopic analysis of the intact brain

Overview of optical BCI research at NUI Maynooth

A brain-computer interface (BCI) is a device that provides a user with an alternative means of interactive communication, rather than the usual modes via physical gestures/speech. Thus it acts as a neural prosthesis bypassing the normal output pathways of the brain, i.e. spinal cord and periphery cascade. An optical BCI uses optical means of determining the user's mental intent, e.g. to turn on a light switch, by spectroscopic analysis of the intact brain

A Concept for Extending the Applicability of Constraint-Induced Movement Therapy through Motor Cortex Activity Feedback Using a Neural Prosthesis

This paper describes a concept for the extension of constraint-induced movement therapy (CIMT) through the use of feedback of primary motor cortex activity. CIMT requires residual movement to act as a source of feedback to the patient, thus preventing its application to those with no perceptible movement. It is proposed in this paper that it is possible to provide feedback of the motor cortex effort to the patient by measurement with near infrared spectroscopy (NIRS). Significant changes in such effort may be used to drive rehabilitative robotic actuators, for example. This may provide a possible avenue for extending CIMT to patients hitherto excluded as a result of severity of condition. In support of such a paradigm, this paper details the current status of CIMT and related attempts to extend rehabilitation therapy through the application of technology. An introduction to the relevant haemodynamics is given including a description of the basic technology behind a suitable NIRS system. An illustration of the proposed therapy is described using a simple NIRS system driving a robotic arm during simple upper-limb unilateral isometric contraction exercises with healthy subjects

Triple wavelength LED driver for optical brain–computer interfaces

A dedicated triple wavelength LED driver is presented for optical brain–computer interfacing (BCI). The solution caters for the constraints of a common-anode grounded case and modulation up to several kilohertz that allows source separation of light that has backscattered from the brain. With total harmonic distortion of 0.95% and a frequency range of ~40 kHz, the driver has application in a continuous wave optical BCI. Other modulation strategies such as time division multiplexing (TDM) are catered for, owing to input DC coupling. Linearity in the optical output is maintained by the ‘load sensing’ differential op-amp on the LED’s current limiting resistor, which is the basis for the V-I conversion

Triple wavelength LED driver for optical brain–computer interfaces

A dedicated triple wavelength LED driver is presented for optical brain–computer interfacing (BCI). The solution caters for the constraints of a common-anode grounded case and modulation up to several kilohertz that allows source separation of light that has backscattered from the brain. With total harmonic distortion of 0.95% and a frequency range of ~40 kHz, the driver has application in a continuous wave optical BCI. Other modulation strategies such as time division multiplexing (TDM) are catered for, owing to input DC coupling. Linearity in the optical output is maintained by the ‘load sensing’ differential op-amp on the LED’s current limiting resistor, which is the basis for the V-I conversion

Optical Safety Assessment of a Near-Infrared Brain-Computer Interface

This paper describes a safety assessment study of near-infrared sources used in an optical brain-computer interface (BCI). The measurement elements of an optical BCI consist of sets of optical sources and detectors. Our current system utilises sources which comprise of dual wavelength light emitting diodes (LED) at 760nm and 880nm. An optical analysis demonstrated that NIR radiation is a negligible source of heating in this case. LED heat conduction however is a major source of heating, and LEDs, though much safer than laser diodes, have been known to cause burns if improperly used. We describe a procedure by which we measure the heat conduction effect of LEDs. We show that the LED systems used in our current generation BCI produce safe levels of thermal energy and are within published safety levels