38 research outputs found
The Inner Life of Bursts
In the thalamus, bursts and single spikes are elicited by distinct visual stimuli, suggesting distinct visual functions. In this issue of Neuron, Wang etĀ al. make use of intracellular recordings of thalamic neurons in vivo to provide a clear, detailed explanation of how natural stimuli are converted intoĀ a neural code that uses both bursts and single spikes
Dorsal lateral geniculate substructure in the Long-Evans rat: A cholera toxin B-subunit study
This study describes the substructure of the dorsal lateral geniculate
nucleus of the thalamus of the pigmented rat (Rattus norvegicus) based on the
eye-of-origin of its retinal ganglion cell inputs. We made monocular
intra-ocular injections of the B-subunit of cholera toxin (CTB), a sensitive
anterograde tracer, in three adult male Long-Evans rats. In four additional
subjects, we injected fluorophor-conjugated CTB in both eyes, using a different
fluorophor in each eye. Brains of these subjects were fixed and sectioned, and
the labeled retinal ganglion cell termini were imaged with wide-field
sub-micron resolution slide scanners. Retinal termination zones were traced to
reconstruct a three dimensional model of the ipsilateral and contralateral
retinal termination zones in the dLGN on both sides of the brain. The dLGN
volume was 1.58 \pm0.094 mm^{3}, comprising 70 \pm 3% the volume of the entire
retinorecipient LGN. We find the retinal terminals to be well-segregated by eye
of origin. We consistently found three or four spatially separated
ipsilateral-recipient zones within each dLGN, rather than the single compact
zone expected. It remains to be determined whether these subdomains represent
distinct functional sublaminae
Speed and Accuracy of Static Image Discrimination by Rats
When discriminating dynamic noisy sensory signals, human and primate subjects
achieve higher accuracy when they take more time to decide, an effect
attributed to accumulation of evidence over time to overcome neural noise. We
measured the speed and accuracy of twelve freely behaving rats discriminating
static, high contrast photographs of real-world objects for water reward in a
self-paced task. Response latency was longer in correct trials compared to
error trials. Discrimination accuracy increased with response latency over the
range of 500-1200ms. We used morphs between previously learned images to vary
the image similarity parametrically, and thereby modulate task difficulty from
ceiling to chance. Over this range we find that rats take more time before
responding in trials with more similar stimuli. We conclude that rats'
perceptual decisions improve with time even in the absence of temporal
information in the stimulus, and that rats modulate speed in response to
discrimination difficulty to balance speed and accuracy
Rational regulation of water-seeking effort in rodents
In the laboratory, animals' motivation to work tends to be positively correlated with reward magnitude. But in nature, rewards earned by work are essential to survival (e.g., working to find water), and the payoff of that work can vary on long timescales (e.g., seasonally). Under these constraints, the strategy of working less when rewards are small could be fatal. We found that instead, rats in a closed economy did more work for water rewards when the rewards were stably smaller, a phenomenon also observed in human labor supply curves. Like human consumers, rats showed elasticity of demand, consuming far more water per day when its price in effort was lower. The neural mechanisms underlying such "rational" market behaviors remain largely unexplored. We propose a dynamic utility maximization model that can account for the dependence of rat labor supply (trials/day) on the wage rate (milliliter/trial) and also predict the temporal dynamics of when rats work. Based on data from mice, we hypothesize that glutamatergic neurons in the subfornical organ in lamina terminalis continuously compute the instantaneous marginal utility of voluntary work for water reward and causally determine the amount and timing of work
Training Rats Using Water Rewards Without Water Restriction
High-throughput behavioral training of rodents has been a transformative development for systems neuroscience. Water or food restriction is typically required to motivate task engagement. We hypothesized a gap between physiological water need and hedonic water satiety that could be leveraged to train rats for water rewards without water restriction. We show that when Citric Acid (CA) is added to water, female rats drink less, yet consume enough to maintain long term health. With 24 h/day access to a visual task with water rewards, rats with ad lib CA water performed 84% Ā± 18% as many trials as in the same task under water restriction. In 2-h daily sessions, rats with ad lib CA water performed 68% Ā± 13% as many trials as under water restriction. Using reward sizes <25 Ī¼l, rats with ad lib CA performed 804 Ā± 285 trials/day in live-in sessions or 364 Ā± 82 trials/day in limited duration daily sessions. The safety of CA water amendment was previously shown for male rats, and the gap between water need and satiety was similar to what we observed in females. Therefore, it is likely that this method will generalize to male rats, though this remains to be shown. We conclude that at least in some contexts rats can be trained using water rewards without water restriction, benefitting both animal welfare and scientific productivity
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Is N-Hacking Ever OK? The consequences of collecting more data in pursuit of statistical significance
Upon completion of an experiment, if a trend is observed that is "not quite significant," it can be tempting to collect more data in an effort to achieve statistical significance. Such sample augmentation or "N-hacking" is condemned because it can lead to an excess of false positives, which can reduce the reproducibility of results. However, the scenarios used to prove this rule tend to be unrealistic, assuming the addition of unlimited extra samples to achieve statistical significance, or doing so when results are not even close to significant; an unlikely situation for most experiments involving patient samples, cultured cells, or live animals. If we were to examine some more realistic scenarios, could there be any situations where N-hacking might be an acceptable practice? This Essay aims to address this question, using simulations to demonstrate how N-hacking causes false positives and to investigate whether this increase is still relevant when using parameters based on real-life experimental settings