Summary Basal forebrain cholinergic neurons constitute a major neuromodulatory system implicated in normal cognition and neurodegenerative dementias. Cholinergic projections densely innervate neocortex, releasing acetylcholine to regulate arousal, attention and learning. However, their precise behavioral function is poorly understood because identified cholinergic neurons have never been recorded during behavior. To determine which aspects of cognition their activity might support we recorded cholinergic neurons using optogenetic identification in mice performing an auditory detection task requiring sustained attention. We found that a non-cholinergic basal forebrain population — but not cholinergic neurons — were correlated with trial-to-trial measures of attention. Surprisingly, cholinergic neurons responded to reward and punishment with unusual speed and precision (18±3ms). Cholinergic responses were scaled by the unexpectedness of reinforcement and were highly similar across neurons and two nuclei innervating distinct cortical areas. These results reveal that the cholinergic system broadcasts a rapid and precisely timed reinforcement signal supporting fast cortical activation and plasticity.

The fastest and most manoeuvrable terrestrial animals are found in savannah habitats, where predators chase and capture running prey. Hunt outcome and success rate are critical to survival, so both predator and prey should evolve to be faster and/or more manoeuvrable. Here we compare locomotor characteristics in two pursuit predator-prey pairs, lion-zebra and cheetah-impala, in their natural savannah habitat in Botswana. We show that although cheetahs and impalas were universally more athletic than lions and zebras in terms of speed, acceleration and turning, within each predator-prey pair, the predators had 20% higher muscle fibre power than prey, 37% greater acceleration and 72% greater deceleration capacity than their prey. We simulated hunt dynamics with these data and showed that hunts at lower speeds enable prey to use their maximum manoeuvring capacity and favour prey survival, and that the predator needs to be more athletic than its prey to sustain a viable success rate.

A defining feature of adaptive behavior is our ability to change the way we interpret sensory stimuli depending on context. Rapid adaptation in behavior has been attributed to frontal cortical circuits, but it is not clear if sensory cortexes also play an essential role in such tasks. In this study we tested whether the auditory cortex was necessary for rapid adaptation in the interpretation of sounds. We used a two-alternative choice sound-categorization task for rats in which the boundary that separated two acoustic categories changed several times within a behavioral session. These shifts in the boundary resulted in changes in the rewarded action for a subset of stimuli. We found that extensive lesions of the auditory cortex did not impair the ability of rats to switch between categorization contingencies and sound discrimination performance was minimally impaired. Similar results were obtained after reversible inactivation of the auditory cortex with muscimol. In contrast, lesions of the auditory thalamus largely impaired discrimination performance and, as a result, the ability to modify behavior across contingencies. Thalamic lesions did not impair performance of a visual discrimination task, indicating that the effects were specific to audition and not to motor preparation or execution. These results suggest that subcortical outputs of the auditory thalamus can mediate rapid adaptation in the interpretation of sounds.

Large mammals that live in arid/desert environments can cope with seasonal and local variations in rainfall, food and climate 1 by moving long distances, often without reliable water or food en route. An animal's capacity for this long distance travel is substantially dependent on the rate of energy utilisation and hence heat production during locomotion-the cost of transport, COT 2-4. Terrestrial COT is much higher than for flying (7.5 times) and swimming (20 times) 4. Terrestrial migrants are usually large 1,2,3 with anatomical specialisations for economical locomotion 5-9 because COT reduces with increasing size and limb length 5,6,7. Here we used GPS tracking collars 10 with movement and environmental sensors to show that blue wildebeest (Connochaetes taurinus, 220 kg) living in a hot arid environment in Northern Botswana walked up to 80 km over five days without drinking. They predominantly travelled during the day and locomotion appeared unaffected by temperature and humidity although some behavioural thermoregulation was apparent. We measured power and efficiency of work production (mechanical work and heat production) during cyclic contractions of intact muscle biopsies from flexor carpi ulnaris of wildebeest and domestic cows (Bos taurus, 760 kg), a comparable sedentary ruminant. The energetic costs of isometric contraction (activation and force generation) in wildebeest and cows were similar to published values for smaller mammals. Wildebeest muscle was substantially more efficient (62.6%) than the same muscle from substantially larger cows (41.8%) and comparable measurements made in smaller mammals (mouse 34% 11 , rabbit 27%). These are the first direct energetic measurements on intact muscle fibres from large mammals and we use them to model the contribution of high working efficiency of wildebeest muscle to minimising thermoregulatory challenge during their long migrations under hot arid conditions. We set out to test the hypothesis that wildebeest undertake long-range locomotion from grazing sites to water sources and that their muscle is optimised to deliver a low COT. We chose blue wildebeest living in the Makgadikgadi Pans National Park in Botswana because water is sparse and in known locations and grazing limited. Wildebeest were captured by darting from a helicopter and fitted with tracking collars of our own design 10 containing GPS, 3D accelerometer, 3D gyroscope, 3D magnetometer, a humidity sensor and a black globe thermometer 12 (to measure combined effect of solar radiation, air temperature and air velocity for the animal) (Fig. 1a, Methods). Collar mass was 1050 g, 0.5% of body mass. After 18 months collars released automatically, dropoff failures were recovered by re-darting, and 17 of the 20 deployed collars were recovered (to date) Barclay for helping us fabricate the thermocouple elements. Field assistants Naomi Terry and Megan Claase. Anna Wilson for logistical support and editorial contributions. Michael Flyman, Department of Wildlife and National Parks for his support and enthusias...