THE PIG AS A MODEL ANIMAL FOR STUDYING COGNITION AND NEUROBEHAVIORAL DISORDERS

Transcription

1 THE PIG AS A MODEL ANIMAL FOR STUDYING COGNITION AND NEUROBEHAVIORAL DISORDERS Elise T. Gieling Utrecht University, Faculty of Veterinary Medicine, Department of Farm Animal Health, Emotion and Cognition Group, the Netherlands CAH Vilentum University of Applied Science, Almere, the Netherlands e.gieling@cahvilentum.nl

2 The pig as a model animal in neurobehavioural research a developmental animal model (early development) an animal model of psychiatric disorders Prerequesits high resemblence with humans species specific knowledge suitable test methods focus on cognitive testing

3 Resemblance with humans

4 Psychiatric disorders The pig as a animal model for Schizophrenia (amphetamine) Depression (chronic stress) Eating disorders: obesity

5 The pig as a developmental animal model early development Hypoxia-ischemia Birth weight-iugr Short follow up-time

6 Species specific knowledge Species-specific opportunities and constraints Visual and olfactory capacities Auditory capacities Gustatory preferences Fysical (in)capabilities Somatosensory information Lacking!

7 General features domestic pig Domesticated years ago Wild boar as ancestor Highly social Daily activities synchronized with sunrise and sunset Active around 65% of time Moving during foraging Searching for food under the surface with muzzle Wallowing (lack of sweat glands)

8 Visual and olfactory capacities Limited and contradictory Pigs learn olfactory discrimination faster than visual and auditory discrimination Large individual variations Odour cues easy to detect Visual acuity lower than in humans Small symbol sizes more difficult Red-green colourblindness is suggested

9 Auditory capacities Hearing range 42-40,5000 Hz Humans 31-17,600 Hz Social vocalization is important in providing information about: Sender Arousal state

10 Gustatory preferences Pigs like sweet tastes According to literature quinine solution is avoided Quinine soaked almonds eaten without problem!!

11 Criteria behavioural task for pigs 1) Healthy unimpaired animals 2) Allow for detailed analysis of behaviour 3) As stress-free as possible 4) Tap ecologically relevant behaviour 5) Standardization 6) Automation 7) Allow investigation of developmental effects 8) Complex and sensitive enough

12 This also accounts for cognitive testing cognition is not a unitary function involves multiple and dissociable systems that interact in cognitive processes Wealth of learning and memory tests available Mainly for rodents: well validated tests Many not suited for / adapted to pigs

13 Classification Classical conditioning studies Pavlovian conditioning Operant conditioning (most) Learning through an aversive or appetitive reinforcer Repeated reinforcements increase respons Yerkes and Coburn 1915

14 Reinforcers Food (with and without food deprivation) Drawback: lack of apetite Social company Access to the group Access to the sow Electrick shock Time out Light (when in darkness) Confinement A dry area (in case of a water maze) Heat

15 How rewards can be obtained Very important! Pigs have evolved to use their snout and root Body not designed to make subtle movements Required action should match one or more of the pigs natural behaviours The pig should naturally understand the task Facilitates learning Keeps animal motivated

16 Operant conditioning tasks Spatial tasks Animal must remember list of places already visited to avoid revisits The use of mazes Alley mazes Fixed starting position One fixed route to goal Wrong alleys should be avoided Free choice mazes Rewards can be found in several places Animal is free to visit and revisit all places Visit order is free Most efficient: visit all bated places once

17 Operant conditioning tasks Spatial tasks Working memory holds list of visits within one trial = short term memory, trial dependant Reference memory holds information about the location the food can be found = long term memory, information gathered over trials Can both be assessed in free-choice mazes Most T or Y mazes: not based on orientation of animal in space not spatial but operant or social

18 Operant conditioning tasks Spatial task with pigs Morris watermaze-like task (Siegford et al 2008) Foraging arena s Hidden food trough's (Mendl et al 1997; Sneddon et al 2000) Depends on nr. of trough's Rooms with food rewards (Yerkes and Coburn 1918; Hagl et al. 2005) Difficult, except for most left/right and middle Radial arm maze (Laughlin et al. 1999) Repeated food search after retention interval with(out) disturbance factor

19 Operant conditioning tasks Spatial tasks for pigs Cognitive Pig Holeboard (Arts et al 2009; Gieling et al 2012, 2013, 2013 in press) Hidden food rewards (4 out of 16 options) can be found by lifting balls with snout Symmetric arena with extra-maze cues for orientation Size and reward choice depending on size/age pigs

20 Operant conditioning tasks Recognition tasks Object Recognition Task (ORT) assesses trial-unique memory based on known preference of rodents to explore unknown objects more than familiar ones Simultaneous recognition Often social recognition, Y-maze Social learning Learning from conspecifics the capability to imitate a demonstrator s behavior

21 Operant conditioning tasks ORT in pigs contradictory results: Memory for novel objects at least 1h (Moustgaard et al. 2002; Kornum 2007) Novelty preference not shown (Gifford 2005; Gifford et al 2007)

22 Operant conditioning tasks Lever pressing tasks (and comparable) Skinner box-like tasks Several reward-schemes possible Equipment should be adapted to species

23 Operant conditioning tasks Lever pressing tasks (and comparable) Panel switching (Kennedy and Baldwin 1972) Progressive ratio (Kennedy and Baldwin 1972; Sneddon et al 2000; Ferguson et al 2009) Fixed ratio (Baldwin and Stephens 1973) Temporal response differentation training (Ferguson et al 2009) Hold lever (min 10s max 14s) Incremental repeated acquisition (Ferguson et al 2009) Press levers in specific order

24 Operant conditioning tasks Reveral learning Rewarding the previously unrewarded option/response Reversal is applied after the animal shows a good performance on the initial aqcuisition Discrimination learning Rewarding one of the 1-X choices an animal can make Generally daily sessions of multiple trials

25 Operant conditioning tasks Reversal learning Discrimination reversal test (Lien and Klopfer 1987) T-maze reversal learning (Bolhuis et al 2004) Low and high responders (coping style) different performance Intra-maze change applied: novel object Reversal can also be applied in a spatial task!

26 Operant conditioning tasks Discrimination learning T-maze discrimination test (colours) (Tanida et al 1991) Y-maze discrimination test (handler discrimination) (Tanida & Nagano 1998; Koba and Tanida 1999) Human approach test: behaviours directed towards humans (Hemsworth et al 1996) Multiple-choice discrimination (colours and olfactory stimuli) (Croney et al 2003) 2-10 choices Correct response reinforced with clicker followed by food reward Non-spatial radial arm maze (Wang et al 2007) Visual cues marked the arms

27 Task choice Studying one or more aspects of cognition? Spatial tasks come closest to the list of criteria mentioned earlier Especially free-choice mazes Mimic natural foraging behaviour, less motivational problems Several behavioural domains can be measured (cognitive, sensory, motor domains) With minor adaptations tasks can be made suitable for measuring other cognitive domains A spatial task could be made a discrimination learning task

28 Final remarks Tasks should reflect range of natural abilities of species Performing under stress/arousal: Influences or impairs memory (Schwabe and Wolf 2010) disrupts cognitive processes (Mendl 1999) Negative reinforcers? Habituation! Little factual knowledge about sensory capacities A lot of tasks applied once; very little replication and validation

29 Thank you Do not all invent your own task but use and improve what is out there! This will improve reliability and validity of cognitive testing of pigs References The Pig as a Model Animal for Studying Cognition and Neurobehavioral Disorders. Elise Titia Gieling Teun Schuurman Rebecca Elizabeth Nordquist Franz Josef van der Staay. Curr Topics Behav Neurosci (2010), DOI /7854_2010_112 # Springer Verlag Berlin Heidelberg Assessing learning and memory in pigs. Elise Titia Gieling Rebecca Elizabeth Nordquist Franz Josef van der Staay. Anim Cogn (2011) 14: DOI /s