Megan Halloran - Academia.edu (original) (raw)
Papers by Megan Halloran
Journal of experimental psychology. Animal learning and cognition, 2020
The midsession reversal task involves a simple simultaneous discrimination in which, each session... more The midsession reversal task involves a simple simultaneous discrimination in which, each session, choice of 1 stimulus (S1) is correct for the first 40 trials of each session, and choice of the other stimulus (S2) is correct for the remaining 40 trials. After considerable training with this task, pigeons typically continue to choose S2 too early (making anticipatory errors) and continue choosing S1 for following the reversal (making perseverative errors). Errors can be reduced, however, by decreasing the probability of reinforcement for correct S2 choices or by increasing the response requirement for S2 choices. Increasing the number of S2 stimuli (over trials, 1 S2 stimulus on each trial), however, does not reduce errors. Instead, it results in an increase in anticipatory errors but no change in perseverative errors. In the present experiment, we increased the number of S1 stimuli (over trials, 1 S1 stimulus on each trial) and found an increase in the number of perseverative error...
G3: Genes|Genomes|Genetics, 2021
Septins are GTP-binding proteins conserved across metazoans. They can polymerize into extended fi... more Septins are GTP-binding proteins conserved across metazoans. They can polymerize into extended filaments and, hence, are considered a component of the cytoskeleton. The number of individual septins varies across the tree of life—yeast (Saccharomyces cerevisiae) has seven distinct subunits, a nematode (Caenorhabditis elegans) has two, and humans have 13. However, the overall geometric unit (an apolar hetero-octameric protomer and filaments assembled there from) has been conserved. To understand septin evolutionary variation, we focused on a related pair of yeast subunits (Cdc11 and Shs1) that appear to have arisen from gene duplication within the fungal clade. Either Cdc11 or Shs1 occupies the terminal position within a hetero-octamer, yet Cdc11 is essential for septin function and cell viability, whereas Shs1 is not. To discern the molecular basis of this divergence, we utilized ancestral gene reconstruction to predict, synthesize, and experimentally examine the most recent common a...
OF THESIS THE MIDSESSION REVERSAL TASK WITH PIGEONS: EFFECTS OF A BRIEF DELAY BETWEEN CHOICE AND ... more OF THESIS THE MIDSESSION REVERSAL TASK WITH PIGEONS: EFFECTS OF A BRIEF DELAY BETWEEN CHOICE AND REINFORCEMENT During a midsession reversal task, the session begins with a simple simultaneous discrimination in which one stimulus (S1) is correct and the alternate stimulus (S2) is incorrect (S1+/S2-). At the halfway point, the discrimination reverses and S2 becomes the correct choice (S2+/S1-). When choosing optimally, a pigeon should choose S1 until the first trial in which it is not reinforced and then shift to S2 (win-stay/lose-shift). With this task pigeons have been shown to respond suboptimally by anticipating the reversal (anticipatory errors) and continuing to choose S1 after the reversal (perseverative errors). This suboptimal behavior may result from a pigeon’s relative impulsivity due to the immediacy of reinforcement following choice. In other choice tasks, there is evidence that the introduction of a short delay between choice and reinforcement may decrease pigeons’ impul...
Microscopy and Microanalysis
The septin proteins are a conserved cytoskeletal element found across eukaryotes (including human... more The septin proteins are a conserved cytoskeletal element found across eukaryotes (including humans) that assemble into filamentous structures in vivo to (i) serve as a barrier between membrane-enclosed compartments, (ii) assist in promoting membrane curvature, and (iii) recruit and bind many non-septin protein targets [1-2]. In Saccharomyces cerevisiae there are five mitotically-expressed septins that are organized into the linear arrangement ("octamer") of Cdc11-Cdc12-Cdc3-Cdc10-Cdc10-Cdc3-Cdc12-Cdc11 (with the terminal Cdc11 replaced with an alternate subunit, Shs1) [3]. Previous reports have suggested that nearly 100 other proteins are localized to the division site (bud neck) and may interact with the septins [2]. However, it remains unknown what contingent of proteins physically interacts with the septin structure, and if so, which position(s) along the length of the octamer are occupied. Previously, we demonstrated the use of a tripartite split GFP system to detect protein-protein interactions between nearby septin subunits and four non-septin binding partners [4-5]. Here, we have screened 25 additional candidates using this method by fluorescence microscopy in live cells.
Journal of experimental psychology. Animal learning and cognition, 2020
The midsession reversal task involves a simple simultaneous discrimination in which, each session... more The midsession reversal task involves a simple simultaneous discrimination in which, each session, choice of 1 stimulus (S1) is correct for the first 40 trials of each session, and choice of the other stimulus (S2) is correct for the remaining 40 trials. After considerable training with this task, pigeons typically continue to choose S2 too early (making anticipatory errors) and continue choosing S1 for following the reversal (making perseverative errors). Errors can be reduced, however, by decreasing the probability of reinforcement for correct S2 choices or by increasing the response requirement for S2 choices. Increasing the number of S2 stimuli (over trials, 1 S2 stimulus on each trial), however, does not reduce errors. Instead, it results in an increase in anticipatory errors but no change in perseverative errors. In the present experiment, we increased the number of S1 stimuli (over trials, 1 S1 stimulus on each trial) and found an increase in the number of perseverative error...
G3: Genes|Genomes|Genetics, 2021
Septins are GTP-binding proteins conserved across metazoans. They can polymerize into extended fi... more Septins are GTP-binding proteins conserved across metazoans. They can polymerize into extended filaments and, hence, are considered a component of the cytoskeleton. The number of individual septins varies across the tree of life—yeast (Saccharomyces cerevisiae) has seven distinct subunits, a nematode (Caenorhabditis elegans) has two, and humans have 13. However, the overall geometric unit (an apolar hetero-octameric protomer and filaments assembled there from) has been conserved. To understand septin evolutionary variation, we focused on a related pair of yeast subunits (Cdc11 and Shs1) that appear to have arisen from gene duplication within the fungal clade. Either Cdc11 or Shs1 occupies the terminal position within a hetero-octamer, yet Cdc11 is essential for septin function and cell viability, whereas Shs1 is not. To discern the molecular basis of this divergence, we utilized ancestral gene reconstruction to predict, synthesize, and experimentally examine the most recent common a...
OF THESIS THE MIDSESSION REVERSAL TASK WITH PIGEONS: EFFECTS OF A BRIEF DELAY BETWEEN CHOICE AND ... more OF THESIS THE MIDSESSION REVERSAL TASK WITH PIGEONS: EFFECTS OF A BRIEF DELAY BETWEEN CHOICE AND REINFORCEMENT During a midsession reversal task, the session begins with a simple simultaneous discrimination in which one stimulus (S1) is correct and the alternate stimulus (S2) is incorrect (S1+/S2-). At the halfway point, the discrimination reverses and S2 becomes the correct choice (S2+/S1-). When choosing optimally, a pigeon should choose S1 until the first trial in which it is not reinforced and then shift to S2 (win-stay/lose-shift). With this task pigeons have been shown to respond suboptimally by anticipating the reversal (anticipatory errors) and continuing to choose S1 after the reversal (perseverative errors). This suboptimal behavior may result from a pigeon’s relative impulsivity due to the immediacy of reinforcement following choice. In other choice tasks, there is evidence that the introduction of a short delay between choice and reinforcement may decrease pigeons’ impul...
Microscopy and Microanalysis
The septin proteins are a conserved cytoskeletal element found across eukaryotes (including human... more The septin proteins are a conserved cytoskeletal element found across eukaryotes (including humans) that assemble into filamentous structures in vivo to (i) serve as a barrier between membrane-enclosed compartments, (ii) assist in promoting membrane curvature, and (iii) recruit and bind many non-septin protein targets [1-2]. In Saccharomyces cerevisiae there are five mitotically-expressed septins that are organized into the linear arrangement ("octamer") of Cdc11-Cdc12-Cdc3-Cdc10-Cdc10-Cdc3-Cdc12-Cdc11 (with the terminal Cdc11 replaced with an alternate subunit, Shs1) [3]. Previous reports have suggested that nearly 100 other proteins are localized to the division site (bud neck) and may interact with the septins [2]. However, it remains unknown what contingent of proteins physically interacts with the septin structure, and if so, which position(s) along the length of the octamer are occupied. Previously, we demonstrated the use of a tripartite split GFP system to detect protein-protein interactions between nearby septin subunits and four non-septin binding partners [4-5]. Here, we have screened 25 additional candidates using this method by fluorescence microscopy in live cells.