Supermassive Black-hole Demographics & Environments With Pulsar Timing Arrays

Precision timing of large arrays (>50) of millisecond pulsars will detect the nanohertz gravitational-wave emission from supermassive binary black holes within the next ~3-7 years. We review the scientific opportunities of these detections, the requirements for success, and the synergies with electromagnetic instruments operating in the 2020s.Comment: Submitted to the Astro2020 Decadal Survey. One of 5 core white-papers authored by members of the NANOGrav Collaboration. 9 pages, 2 figure

Task- and Time-Dependent Memory Enhancement by Dehydroepiandosterone in Day-Old Chicks

We have previously reported the presence of dehydroepiandosterone (DHEA) in the dayold- chick brain, and a role for it in enhanced memory formation. Here we confirm that intracerebral injections of DHEA 5 min before training on the weak passive avoidance task enhanced recall 24 hours after training. Recall per se on an appetitive visual categorization task was not altered by administration of DHEA 5 min before training. However administration of DHEA 5 min before limited or very limited training on a visual categorization task (20 or 10 pecks only) appeared to enhance consolidation of this task at test 24 h after training; reducing the latency and total time taken to complete the test (60 pecks), while not detrimentally altering accuracy. Moreover, DHEA is unlikely to induce this effect via possible anxiolytic effects because it did not alter behavior in the open field test. We also examined diffusion of DHEA throughout the brain at various stages following intracerebral injection

Measuring cognitive load and cognition: metrics for technology-enhanced learning

This critical and reflective literature review examines international research published over the last decade to summarise the different kinds of measures that have been used to explore cognitive load and critiques the strengths and limitations of those focussed on the development of direct empirical approaches. Over the last 40 years, cognitive load theory has become established as one of the most successful and influential theoretical explanations of cognitive processing during learning. Despite this success, attempts to obtain direct objective measures of the theory's central theoretical construct – cognitive load – have proved elusive. This obstacle represents the most significant outstanding challenge for successfully embedding the theoretical and experimental work on cognitive load in empirical data from authentic learning situations. Progress to date on the theoretical and practical approaches to cognitive load are discussed along with the influences of individual differences on cognitive load in order to assess the prospects for the development and application of direct empirical measures of cognitive load especially in technology-rich contexts

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Conservation problems and programmes. The giant tortoises. The land iguanas. The Hawaiian petrels. The penguins, cormorants and gulls. The fire ants. The control of introduced mammals. Botany. Marine biology. Galapagos cave faunas. Rare twin births of giant tortoises. Visitors and events at the Charles Darwin Research Station (CDRS)

A behavioural investigation of the function of glycoprotein fucosylation in learning and memory in the day-old domestic chicken.

Two new paradigms of learning in the day-old domestic chick were developed and tested. The first was a serial colour-discrimination passive avoidance task, similar to that used by Gibbs and Ng (1977), in which chicks were trained to discriminate between red and green stimuli by pairing one with the bitter taste of methylanthranilate. The second was a sickness-conditioned aversion task, similar to that developed by Garcia and Ervin (1968), in which chicks were trained to associate pecking at a stimulus with subsequent sickness, induced by lithium chloride injection. 2-Deoxy galactose (2-Dgal), a fucose analogue that inhibits the completion of brain fucosylglycoproteins, induced amnesia for both tasks when injected into both hemispheres of the forebrain before training. Amnesia was similarly induced for the passive avoidance task when 2-Dgal was injected into the right forebrain alone, but not the left forebrain. This indicates that fucosylglycoprotein incorporation has a more important function in the right forebrain after passive avoidance training. No amnesia for the sickness-conditioned aversion task was detected after injection of 2- Dgal into either the left or the right forebrain alone. Thus either hemisphere was capable of learning this task but only one hemisphere was required. 2-Dgal was tested for a state-dependent action in both learning paradigms, by readministration of the drug before the retention test, in a 2x2 experimental design. The amnesia was not state-dependent, since readministration of 2-Dgal did not lead to recall of the learned response in either task. Thus the amnesia was not due to learned information becoming cue-dependent. Instead, amnesia was caused by the direct interruption of molecular processes necessary for memory formation. The results are discussed in the context of previous biochemical and morphological findings concerning fucosylglycoprotein incorporation and synaptic remodeling

216 Jewish Hospital of St. Louis

https://digitalcommons.wustl.edu/bjc_216/1186/thumbnail.jp

An Investigation of the Neurophysiological Correspondents of Learning and Memory in Two Forebrain Regions of the Day-Old Chick

Spontaneous bursting (5 or more spikes of 200-450mV amplitude at 400Hz) occurs in many areas of chick forebrain. Day-old chicks trained on a one-trial passive avoidance task show a bilateral increase of up to 350% in bursting following training in one of these areas: the intermediate medial hyperstriatum ventrale, or IMHV (Mason & Rose, 1987; 1988). An investigation was carried out into the time course and lateralization of this change in bursting activity following the training of day-old chicks on a passive avoidance task. Chicks were trained to either avoid a bead coated with the bitter-tasting substance methylanthranilate (M-birds) or were trained to peck a water coated bead (W-birds). Bursting was recorded sequentially from the IMHV of both hemispheres at 8 time points over the period 1 to 9 hours post-test. The results indicate that there are significant differences in bursting activity recorded from M-birds only during the period 3-7hr posttest, when compared to W-birds. Between 6-7hr posttest there are significant differences in the burst firing patterns of the right IMHV of M-birds compared to the left. At other time points tested there are no significant differences between hemispheres. No between hemisphere differences are evident in W-birds. Multi-unit recordings were made from the lobus parolfactorius (LPO), another forebrain structure to show changes in biochemistry and morphology following passive avoidance training. M-birds showed a higher incidence of bursting when compared to W-birds over the period 1-10hr posttest. No lateralization of bursting was seen in either group at any time posttest. In a further experiment, chicks trained to avoid the methylanthranilate coated bead were subjected to subconvulsive electroshock 5min posttraining. This procedure was used to test whether the training-induced increase in bursting in the LPO was a direct correlate of memory formation for the task. This electroshock treatment produced two groups of birds: one group that avoided the bead (remembered the task) and another that pecked the bead (forgot the task). Multi-unit recordings from the LPO of these two groups revealed that the group that avoided the bead had a significantly higher mean burst-frequency when compared to the group that pecked the bead, indicating that increased bursting in the LPO following training is directly associated with recall for the task. These results are similar to those of Mason and Rose (1988) who showed that amnesia abolished a training-induced enhancement of bursting in the IMHV. The effects of pretraining bilateral LPO lesions on IMHV bursting activity were examined. The IMHV of four groups of birds was recorded ftom following training: two groups of M-birds, one with LPO lesions the other with sham LPO lesions and two similarly treated groups of W-birds. A significant increase in overall IMHV bursting activity was observed in sham-lesioned M-birds when compared to sham-lesioned W-birds. However, no significant difference in bursting activity was seen between lesioned M-birds and lesioned W-birds. There was a trend towards a higher overall level of bursting in lesioned W-birds, when compared to sham-lesioned W-birds. These results are discussed with reference to previous electrophysiological studies concerning the role of burst-firing patterns in models of learning and memory