Adaptive forgetting of place/object memory for dung in the domestic horse (Equus ferus caballus): Memory for a day.

The domestic horse (Equus ferus caballus) makes dung deposits to form "stud-piles" and compulsively examines dung droppings, suggesting that dung contains species-relevant information. The present study investigates horses' use of location (place), odor (object) and memory for dung sniff encounters. Horses were video recorded in 2 indoor and 4 outdoor riding arenas as they were taken at different time intervals to experimenter-determined objects or dung deposits that they could sniff. Frame-by-frame video analysis measured approaches, sniff duration, nostril use, ear position and blinking associated with dung investigation. Horses approached and sniffed dung-deposits for longer duration than non-dung objects in all test locations. They made head movements across the extent of dung-deposits when sniffing, showed no nostril or ear preference directed to the target, and blinked as they disengage from sniffing. Reduced approach probability and sniff duration showed that they displayed good place/object memory for dung previously visited at similar and different locations on the same day but poor memory for dung visited on a previous day. Adaptive forgetting of object/place memory for dung after a previous day's dung visit may optimizes risk assessment, including the possibility of premature interruption of foraging by conspecifics.

Correction: Data-driven analyses of motor impairments in animal models of neurological disorders.

[This corrects the article DOI: 10.1371/journal.pbio.3000516.].

Cortical network and projection neuron types that articulate serial order in a skilled motor behavior.

Skilled motor behaviors require orderly coordination of multiple constituent movements with sensory cues towards achieving a goal, but the underlying brain circuit mechanisms remain unclear. Here we show that target-guided reach-grasp-to-drink (RGD) in mice involves the ordering and coordination of a set of forelimb and oral actions. Cortex-wide activity imaging of multiple glutamatergic projection neuron (PN) types uncovered a network, involving the secondary motor cortex (MOs), forelimb primary motor and somatosensory cortex, that tracked RGD movements. Photo-inhibition highlighted MOs in coordinating RGD movements. Within the MOs, population neural trajectories tracked RGD progression and single neuron activities integrated across constituent movements. Notably, MOs intratelencephalic, pyramidal tract, and corticothalamic PN activities correlated with action coordination, showed distinct neural dynamics trajectories, and differentially contributed to movement coordination. Our results delineate a cortical network and key areas, PN types, and neural dynamics therein that articulate the serial order and coordination of a skilled behavior.

Weak-hyperactive hippocampal CA1 neurons in the prodromal stage of Alzheimer's disease in hybrid AppNL-G-F/NL-G-F × Thy1-GCaMP6s+/- mice suggest disrupted plasticity.

This study investigated the impact of familial Alzheimer's disease (AD)-linked amyloid precursor protein (App) mutations on hippocampal CA1 neuronal activity and function at an early disease stage in AppNL-G-F/NL-G-F × Thy1-GCaMP6s+/- (A-TG) mice using calcium imaging. Longitudinal assessment of spatial behavior at 12 and 18 months of age identified an early disease stage at 12 months when there was significant amyloid beta pathology with mild behavioral deficits. Hippocampal CA1 neuronal activity and event-related encoding of distance and time were therefore assessed at 12 months of age in several configurations of an air-induced running task to assess the dynamics of cellular activity. Neurons in A-TG mice displayed diminished (weaker) and more frequent (hyperactive) neuronal firing that was more pronounced during movement compared to immobility. Responsive neurons showed configuration-specific deficits in distance and time encoding with impairment in adapting their responses to changing configurations. These results suggest that at an early stage of AD in the absence of full-blown behavioral deficits, weak-hyperactive neuronal activity may induce impairments in sensory perception of changing environments.

Impairments and compensation in string-pulling after middle cerebral artery occlusion in the rat.

Stroke is a leading cause of long-term disability in humans, and it is frequently associated with impairments in the skilled use of the arms and hands. Many human upper limb impairments and compensatory changes have been successfully modeled in rodent studies of neocortical stroke, especially those that evaluate single limb use in tasks, such as reaching for food. Humans also use their hands for bilaterally coordinated movements, dependent upon interhemispheric cortical projections, which are also compromised by unilateral stroke. This study describes middle cerebral artery occlusion (MCAO) dependent changes in the bilaterally dependent hand use behavior of string-pulling in the rat. The task involves making hand-over-hand movements to pull down a string that contains a food reward attached to its end. MCAO rats missed the string more often with both hands than Sham rats. When the string was missed on the contralateral to MCAO body side, rats continued to cycle through subcomponents of string-pulling behavior as if the string were grasped in the hand. Rats also failed to make a grasping motion with the contralateral to MCAO hand when the string was missed and instead, demonstrated an open-handed raking-like motions. Nevertheless, with repeated attempts, rats performed components of string-pulling well enough to obtain a reward on the end of the string. Thus, string-pulling behavior is sensitive to bilateral impairments but is achieved with compensatory adjustments following MCAO. These aspects of MCAO string-pulling provide a foundation for studies that investigate the efficacy of therapeutic intervention which might enhance neuroplasticity and recovery.

Hippocampal conjunctive and complementary CA1 populations relate sensory events to movement.

Hippocampal CA1 neurons respond to sensory stimuli during enforced immobility, movement, and their transitions in a new conveyor belt task. Head-fixed mice were exposed to light flashes or air streams while at rest, spontaneously moving, or running a fixed distance. Two-photon calcium imaging of CA1 neurons revealed that 62% of 3341 imaged cells were active during one or more of 20 sensorimotor events. Of these active cells, 17% were active for any given sensorimotor event, with a higher proportion during locomotion. The study found two types of cells: Conjunctive cells that were active across multiple events, and complementary cells that were active only during individual events, encoding novel sensorimotor events or their delayed repetitions. The configuration of these cells across changing sensorimotor events may signify the role of hippocampus in functional networks integrating sensory information with ongoing movement making it suitable for movement guidance.

Challenges of a small world analysis for the continuous monitoring of behavior in mice.

Documenting a mouse's "real world" behavior in the "small world" of a laboratory cage with continuous video recordings offers insights into phenotypical expression of mouse genotypes, development and aging, and neurological disease. Nevertheless, there are challenges in the design of a small world, the behavior selected for analysis, and the form of the analysis used. Here we offer insights into small world analyses by describing how acute behavioral procedures can guide continuous behavioral methodology. We show how algorithms can identify behavioral acts including walking and rearing, circadian patterns of action including sleep duration and waking activity, and the organization of patterns of movement into home base activity and excursions, and how they are altered with aging. We additionally describe how specific tests can be incorporated within a mouse's living arrangement. We emphasize how machine learning can condense and organize continuous activity that extends over extended periods of time.

A Neural Network Reveals Motoric Effects of Maternal Preconception Exposure to Nicotine on Rat Pup Behavior: A New Approach for Movement Disorders Diagnosis.

Neurodevelopmental disorders can stem from pharmacological, genetic, or environmental causes and early diagnosis is often a key to successful treatment. To improve early detection of neurological motor impairments, we developed a deep neural network for data-driven analyses. The network was applied to study the effect of maternal nicotine exposure prior to conception on 10-day-old rat pup motor behavior in an open field task. Female Long-Evans rats were administered nicotine (15 mg/L) in sweetened drinking water (1% sucralose) for seven consecutive weeks immediately prior to mating. The neural network outperformed human expert designed animal locomotion measures in distinguishing rat pups born to nicotine exposed dams vs. control dams (87 vs. 64% classification accuracy). Notably, the network discovered novel movement alterations in posture, movement initiation and a stereotypy in "warm-up" behavior (repeated movements along specific body dimensions) that were predictive of nicotine exposure. The results suggest novel findings that maternal preconception nicotine exposure delays and alters offspring motor development. Similar behavioral symptoms are associated with drug-related causes of disorders such as autism spectrum disorder and attention-deficit/hyperactivity disorder in human children. Thus, the identification of motor impairments in at-risk offspring here shows how neuronal networks can guide the development of more accurate behavioral tests to earlier diagnose symptoms of neurodevelopmental disorders in infants and children.

Memory for surface objects in an arena by the horse (Equus ferus caballus) under saddle: Evidence for dual process theory of spatial representation.

Place memory, the ability to remember locations, is a feature of many animal species. This episodic-like memory is displayed in the foraging behavior of animals and has been studied in many different kinds of laboratory spatial tasks. A horse stallion, Equus ferus caballus, will create "dung-heaps or stud-piles" by defecation in the same place suggesting that the behavior is central to spatial behavior but to date there has been little investigation of horse olfactory/spatial behavior. The present study describes investigatory behavior of horses for objects on the surface of a riding arena. Horses under saddle approached objects on the arena surface that included small pieces of straw, fur, and paper and larger objects including clumps of debris and were especially interested in dung droppings left by other horses. Once an object was investigated by sniffing, it was usually not approached again during that outing but could be approached anew on the following day. Dung investigatory behavior and place memory were confirmed in a number of structured tests in which test-retest intervals were varied. The results are discussed in relation to the dual process theory that proposes that spatial representations central to adaptive behavior require both allocentric Cartesian spatial information and egocentric episodic-like information.

Learning to cricket hunt by the laboratory mouse (Mus musculus): Skilled movements of the hands and mouth in cricket capture and consumption.

Although the mouse (Mus musculus) is preyed upon by many other species of animals, it is also a predator and will hunt and consume crickets. There has been no previous description of how mice learn to hunt and no report on the extent to which they use their hands and mouth to assist prey capture and these were the objectives of the present study. Mice given one cricket each day displayed decreasing hunt times over 25-days for three phases of a hunt: investigate, in which a mouse explored and periodically encounter a cricket and often bit at it; pursue, in which a mouse's approach remained focused on the cricket until it was captured; and consume, in which the cricket was handled, decapitated, its core eaten, with its shell discarded. Although visual and auditory cues may contribute to locating a cricket, the vibrissae appeared to provide guidance in pursuit and capture when the cricket and mouse were proximate. Cricket capture involved extensive collaborative use of the mouth and the hands and mice could initiate capture with either the mouth or hands. Handling to eat involved manipulating the cricket into a head-up, ventrum-in position for decapitation and selective eating of the core of the cricket. The results are discussed in relation to mouse learning of a complex natural behavior, the use of tactile cues in the species-specific behavior of predation, and the contributions of the hands and mouth to predation.

Does play shape hand use skill in rats?

Hand use is a widespread act in many vertebrate lineages and subserves behaviors including locomotion, predation, feeding, nest construction, and grooming. In order to determine whether hand use is similarly used in social behavior, the present paper describes hand use in the social play of rats. In the course of rough and tumble play sessions, rats are found to make as many as twenty different movements a minute with each hand for the purposes of manipulating a partner into a subordinate position or defending against a partner's attack. The hand movements comprise signaling movements of touching, offensive manipulating of a partner to control a play engagement, and defensive hand movements directed toward blocking, pushing and pulling to parry an attack. For signaling, attack and defense, hand movements have a structure that is similar to the structure of hand movements used for other purposes including eating, but in their contact points on an opponent, they are tailored for partner control. Given the time devoted to play by rats, play likely features the social rat behavior with the most extensive use of hand movements. This extensive use of hand movements for social play is discussed in relation to the ubiquity of hand use in adaptive behavior, the evolution of hand use in the play of mammals, and in relation to extending the multifunctional theory of the purposes of play to include the education of skilled hand movements for various adult functions including as feeding.

Skilled movement and posture deficits in rat string-pulling behavior following low dose space radiation (28Si) exposure.

Deep space flight missions beyond the Van Allen belt have the potential to expose astronauts to space radiation which may damage the central nervous system and impair function. The proposed mission to Mars will be the longest mission-to-date and identifying mission critical tasks that are sensitive to space radiation is important for developing and evaluating the efficacy of counter measures. Fine motor control has been assessed in humans, rats, and many other species using string-pulling behavior. For example, focal cortical damage has been previously shown to disrupt the topographic (i.e., path circuity) and kinematic (i.e., moment-to-moment speed) organization of rat string-pulling behavior count to compromise task accuracy. In the current study, rats were exposed to a ground-based model of simulated space radiation (5 cGy 28Silicon), and string-pulling behavior was used to assess fine motor control. Irradiated rats initially took longer to pull an unweighted string into a cage, exhibited impaired accuracy in grasping the string, and displayed postural deficits. Once rats were switched to a weighted string, some deficits lessened but postural instability remained. These results demonstrate that a single exposure to a low dose of space radiation disrupts skilled hand movements and posture, suggestive of neural impairment. This work establishes a foundation for future studies to investigate the neural structures and circuits involved in fine motor control and to examine the effectiveness of counter measures to attenuate the effects of space radiation on fine motor control.

Cholinergic upregulation by optogenetic stimulation of nucleus basalis after photothrombotic stroke in forelimb somatosensory cortex improves endpoint and motor but not sensory control of skilled reaching in mice.

A network of cholinergic neurons in the basal forebrain innerve the forebrain and are proposed to contribute to a variety of functions including cortical plasticity, attention, and sensorimotor behavior. This study examined the contribution of the nucleus basalis cholinergic projection to the sensorimotor cortex on recovery on a skilled reach-to-eat task following photothrombotic stroke in the forelimb region of the somatosensory cortex. Mice were trained to perform a single pellet skilled reaching task and their pre and poststroke performance, from Day 4 to Day 28 poststroke, was assessed frame-by-frame by video analysis with endpoint, movement and sensorimotor integration measures. Somatosensory forelimb lesions produced impairments in endpoint and movement component measures of reaching and increased the incidence of fictive eating, a sensory impairment in mistaking a missed reach for a successful reach. Upregulated acetylcholine (ACh) release, as measured by local field potential recording, elicited via optogenetic stimulation of the nucleus basalis improved recovery of reaching and improved movement scores but did not affect sensorimotor integration impairment poststroke. The results show that the mouse cortical forelimb somatosensory region contributes to forelimb motor behavior and suggest that ACh upregulation could serve as an adjunct to behavioral therapy for acute treatment of stroke.

Mouse Arm and hand movements in grooming are reaching movements: Evolution of reaching, handedness, and the thumbnail.

Grooming in the mouse features hand licking and symmetric and asymmetric arm and hand "strokes" over the face and body to maintain pelage. Grooming is syntactically organized but the structure of individualized movements of the arm, hand, and tongue have not been examined. Here spontaneous and water-induced grooming was video recorded in free-moving and head-fixed mice and subject to frame-by-frame video inspection and kinematic analysis using Physics Tracker. All groom arm and hand movements had a structure similar to that described for reach-to-eat movements. The movement included the hand lifting from the floor to supinate with the digits flexing and closed to a collect position, an aim position directed to a groom target, an advance to the target during which the fingers extend and open and the hand pronates, a grasp of a target on the snout, nose, or vibrissae, and a withdraw to the mouth where licking occurs, or a return to the starting position. This structure was present in individual unilateral forelimb groom strokes, in bilateral symmetric, or asymmetric groom strokes, and comprised the individuated components of a sequence of groom movements. Reach-to-groom movements could feature an ulnar adduction that positions the ulnar portion of the hand including and the thumb across the eye and nose, a movement that aids Hardarian fluid spreading. It is proposed that the mouse thumb nail is an anatomical feature that minimizes damage to the eye or nose that might be incurred by a claw. This analysis of the reach-to-groom movement provides insights into the flexibility of hand use in adaptive behavior, the evolution of skilled reaching movements, the neural control of reaching movements and the presence of the thumb nail in the mouse.

A Matlab-based toolbox for characterizing behavior of rodents engaged in string-pulling.

String-pulling by rodents is a behavior in which animals make rhythmical body, head, and bilateral forearm as well as skilled hand movements to spontaneously reel in a string. Typical analysis includes kinematic assessment of hand movements done by manually annotating frames. Here, we describe a Matlab-based software that allows whole-body motion characterization using optical flow estimation, descriptive statistics, principal component, and independent component analyses as well as temporal measures of Fano factor, entropy, and Higuchi fractal dimension. Based on image-segmentation and heuristic algorithms for object tracking, the software also allows tracking of body, ears, nose, and forehands for estimation of kinematic parameters such as body length, body angle, head roll, head yaw, head pitch, and path and speed of hand movements. The utility of the task and software is demonstrated by characterizing postural and hand kinematic differences in string-pulling behavior of two strains of mice, C57BL/6 and Swiss Webster.

Sniff, look and loop excursions as the unit of "exploration" in the horse (Equus ferus caballis) when free or under saddle in an equestrian arena.

Spontaneous locomotor behavior in a novel space reveals insights into an animal's world view or Umwelt. For example, in many animal species, spontaneous behavior in a novel environment is parsed into activities at a home base and excursions from the home base. Domestic horses (Equus ferus caballas) are frequently ridden for recreation or in performance events in an equestrian arena but there has been no description of horse behavior in an arena when they are unconstrained and "exploring" or when moving freely under saddle. The present examination of exploration provides insights into horse adaptive behavior more generally as well as insights into horse performance under saddle. Thoroughbred, American Quarter Horse and mixed-breed mares and geldings of various ages, with various degrees of training under saddle, and with varying familiarity with the arena were given 30-min tests in which they were at liberty to explore an equestrian arena. Additional 30-min tests were given in which horses explored the arena containing a tethered partner, or were ridden. Despite breed, sex, age and experience, behavior was similar. A horse spent most of its time near the entrance door of the area where it looked out, paced, and rolled. Periodic excursions formed loops. The outward leg of a loop was slow, often featured sniffing the ground, and ended with a head-raised, ears-forward look toward the far end of the arena. The homeward leg of a loop was made with lowered-head and ears-back and was relatively direct and fast. Successive loops could increase or decrease in size over a test period. If a partner was tethered at the far end of the area, a horse shifted its activity toward the partner. When horses under saddle were asked to make excursions into the arena but otherwise left unconstrained, they made loops, similar to that of freely moving horses. When ridden around the arena they returned more quickly to the near end of the arena than when leaving the near end of the arena. This organized home base/excursion behavior is discussed in relation to horse social structure and to its expression while under saddle.

Low acetylcholine during early sleep is important for motor memory consolidation.

The synaptic homeostasis theory of sleep proposes that low neurotransmitter activity in sleep optimizes memory consolidation. We tested this theory by asking whether increasing acetylcholine levels during early sleep would weaken motor memory consolidation. We trained separate groups of adult mice on the rotarod walking task and the single pellet reaching task, and after training, administered physostigmine, an acetylcholinesterase inhibitor, to increase cholinergic tone in subsequent sleep. Post-sleep testing showed that physostigmine impaired motor skill acquisition of both tasks. Home-cage video monitoring and electrophysiology revealed that physostigmine disrupted sleep structure, delayed non-rapid-eye-movement sleep onset, and reduced slow-wave power in the hippocampus and cortex. Additional experiments showed that: (1) the impaired performance associated with physostigmine was not due to its effects on sleep structure, as 1 h of sleep deprivation after training did not impair rotarod performance, (2) a reduction in cholinergic tone by inactivation of cholinergic neurons during early sleep did not affect rotarod performance, and (3) stimulating or blocking muscarinic and nicotinic acetylcholine receptors did not impair rotarod performance. Taken together, the experiments suggest that the increased slow wave activity and inactivation of both muscarinic and nicotinic receptors during early sleep due to reduced acetylcholine contribute to motor memory consolidation.

The temporal choreography of the yo-yo movement of getting spaghetti into the mouth by the head-fixed mouse.

There is debate over whether single-handed eating movements, reaching for food and withdrawing the hand to place the food in the mouth, originated in the primate lineage or whether they originated in phylogenetically-earlier Euarchontoglires. Most spontaneous hand use in eating by the laboratory mouse (Mus domestica) involves both hands, and a central question is the extent to which the movements are symmetric. Here we describe an asymmetry of spontaneous single hand use by the head-fixed mouse in making the yo-yo hand movement of removing and replacing a piece of pasta (spaghetti) in the mouth for eating. We also describe the problem/solution of placing into the mouth the end of a held item that protrudes at some distance from the hand. Pasta-eating proceeds in bouts, and a bout starts with raising the hands, which are holding a piece of pasta, to place one end of the pasta in the mouth for biting. A bout ends with lowering the hands, still holding the pasta stem, while the pasta morsel that has been bitten off is chewed. Hand-lowering after the pasta is removed from the mouth is slow, concurrent and symmetric, both when the pasta is held by both hands and when it is held in one hand. Hand-raising to place the pasta in the mouth is fast, consecutive and asymmetric, both when the pasta is held in both hands and when it is held in one hand. Frame-by-frame analyses of the video record combined with kinematic analyses show that a preferred single hand not only directs one end of the pasta to the mouth but also readjusts the trajectory of the pasta if it misses the mouth. The specialized use of a single hand by the mouse, even when the hands are bilaterally engaged, and the corrective asymmetric movements with which one hand adjusts the pasta's trajectory with the other hand playing a supporting role, is discussed in relation to the idea that hand preference, specialization, and dexterity have somatosensory and preprimate origins.

Two types of memory-based (pantomime) reaches distinguished by gaze anchoring in reach-to-grasp tasks.

Comparisons of target-based reaching vs memory-based (pantomime) reaching have been used to obtain insight into the visuomotor control of reaching. The present study examined the contribution of gaze anchoring, reaching to a target that is under continuous gaze, to both target-based and memory-based reaching. Participants made target-based reaches for discs located on a table or food items located on a pedestal or they replaced the objects. They then made memory-based reaches in which they pantomimed their target-based reaches. Participants were fitted with hand sensors for kinematic tracking and an eye tracker to monitor gaze. When making target-based reaches, participants directed gaze to the target location from reach onset to offset without interrupting saccades. Similar gaze anchoring was present for memory-based reaches when the surface upon which the target had been placed remained. When the target and its surface were both removed there was no systematic relationship between gaze and the reach. Gaze anchoring was also present when participants replaced a target on a surface, a movement featuring a reach but little grasp. That memory-based reaches can be either gaze anchor-associated or gaze anchor-independent is discussed in relation to contemporary views of the neural control of reaching.

Data-driven analyses of motor impairments in animal models of neurological disorders.

Behavior provides important insights into neuronal processes. For example, analysis of reaching movements can give a reliable indication of the degree of impairment in neurological disorders such as stroke, Parkinson disease, or Huntington disease. The analysis of such movement abnormalities is notoriously difficult and requires a trained evaluator. Here, we show that a deep neural network is able to score behavioral impairments with expert accuracy in rodent models of stroke. The same network was also trained to successfully score movements in a variety of other behavioral tasks. The neural network also uncovered novel movement alterations related to stroke, which had higher predictive power of stroke volume than the movement components defined by human experts. Moreover, when the regression network was trained only on categorical information (control = 0; stroke = 1), it generated predictions with intermediate values between 0 and 1 that matched the human expert scores of stroke severity. The network thus offers a new data-driven approach to automatically derive ratings of motor impairments. Altogether, this network can provide a reliable neurological assessment and can assist the design of behavioral indices to diagnose and monitor neurological disorders.