21 Nov 2020

Enrichment For Rats Part 5 - seeking, pleasure and reward

This is the fifth in a series of six articles about enrichment for rats. Today we are going to explore one of the greatest benefits of enriching our pet rats’ lives – pleasure! As we saw in article one of this series, rats (in common with all mammals) have four top-level emotional systems as described by Panksepp. These are Fear, Rage, Panic, and Seeking.  

The first three are survival systems that cause stress responses in the rat’s body. Seeking is different. It is driven by the body’s pleasure and reward system, and a rat who is seeking is motivated by a felt need (hunger, thirst, lust, cold, loneliness) to search their environment for a solution.  

Finding the solution brings not only relief of the felt need, but a hit of dopamine, serotonin and/or oxytocin. These hormones bring with them the feel-good emotions we describe as relief, excitement, pleasure, joy, connection, and love.  

Pet rats who always have food available in a bowl rarely experience hunger. Adlib feeding is known to reduce health and lifespan as rats age. It also dulls the motivation for seeking food (hunger) and the pleasure responses that come with finding food and relieving hunger.  

Equally, a lack of choice in the environment – such as one type of water source, hammocks but no bedding, one other rat companion, and nothing to aid cooling if they get to warm – leaves the felt need unsatisfied.  

Even when the rat employs seeking behaviour to meet their needs, the environment fails to deliver. This leads to feelings of discomfort and frustration and (from our perspective) opportunities for relief, pleasure, and excitement are missed. 

The mammalian body maintains several balanced systems, which rely on chemical and nervous system sensors and triggers to maintain equilibrium within close parameters. This state of balance in the body is called homeostasis.  

A rat has evolved over millions of years to respond to felt need (on the back of chemical triggers) to energetically explore and investigate their environment, seeking out resources that will meet the need. We call this foraging and our rats are experts!  

It is important to realise that foraging does not mean seeking food but, rather, seeking resources. Rats can forage for bedding, water, shade, shelter, even company. Making this mental leap in understanding the term will help us when it comes to providing a rich and enriching foraging experience.  

The impact of choice 

We talked a bit about choice in article 4 of this series, but now we are ready to explore this in detail. Having choice is essential for allowing our rats – within a limited caged environment – to exercise their preferences and meet their felt needs without frustration.  

In any group of rats there will be individuals with a wide range of physical abilities, problem-solving capabilities, and internal motivations. Some rats will be more (or less) driven to work for food, build nests, bathe in open water sources, and so on.  

Most rats will prefer some foods over others, but not all will favour the same ones. Some will prefer warm rat huddles, even on warm days. Others will decide to sleep alone. Some rats will choose to climb ropes, others will opt for branches every time.  

And these individual differences – that we call preferences – extend to biological, environmental, and experiential disparities that go on to impact what brings each rat the most pleasure and reward.  

So, any individual rat might be highly motivated by wheel running, water play, digging, aerial acrobatics, nest building, gnawing, climbing, humans, or the details of any of these. Most rats are motivated by food, but not all food. All rats have preferences.  

And preferences will – at least to a degree – determine motivation. Is the reward worth the effort? Not if the reward doesn’t motivate you! Physical needs are great motivators – a hungry rat will work for food with enthusiasm and vigour.  

The reward experienced as a result can also be increased by meeting a strongly felt need. Think about the intense pleasure of a cold drink after a walk on a warm day. Or sinking into a comfortable bed at the end of a particularly tiring day.  

Giving your rats some fasting periods when food is unavailable or scarce, increases not only health and longevity, but also the reward experienced when food arrives. Motivation to work for that food, whether foraging around the environment or solving a foraging problem, is raised. 

The Seeking System 

This emotional system is known to be sensitised by: 

  • Homeostatic imbalances (hunger, thirst, thermal imbalance, or sexual frustration). 

  • External stimuli (sensory stimulation, e.g. the smell or sound in the environment that suggests that a felt need could be satisfied). 

  • Learned cues (happenings that herald the availability of food, water, a mate, etc).  

When these three stimuli come together the incentive to forage (seek) is strong. We can use this information to create maximum engagement with any new foraging experience that we introduce to our rats’ environment. 

This system employs both motivation and reward to ensure that the body’s requirements are met. The reward system involves primarily the neurotransmitter, dopamine, but is also affected by serotonin and even oxytocin (if the reward has a social context). 

It remains unclear as to whether these hormones are activated by the act of seeking alone (emotions felt: excitement, anticipation) or by the process of finding (and engaging with) what is needed. Felt need that is followed by seeking and not finding, triggers frustration and anger.  

What is certain is that achieving the goal is accompanied by a significant “feel-good” rush of hormones. Emotions, such as satisfaction and joy, can accompany the comfort that replaces felt need when the need is satisfied. This is often due to the sensory input from the item that is found.  

It is easiest to see this in relation to food. The smell of the food in the environment triggers anticipation and stimulates the salivary glands to start producing saliva. The motivation to search for and work to reach and release the food is high.  

The food is located, the work to reach it begins and the rat’s motivation is at its highest. Success and satisfaction are moments away – and at this point, risks might be taken to obtain the food.  

Once the food is in the rat’s hands and mouth, smell, taste, and texture are all in overdrive and even the acts of licking and gnawing add to the pleasure that is experienced. This is not only pleasure but self-soothing and stress relieving.  

The greater the felt need – and the higher the value of the sought item – the greater the impact on the brain’s reward circuitry. It is easy to see the positive impact that providing this type of enrichment can have.   

The opportunity to seek what is needed from the environment lays down layers of choice and control for the rat, which all adds to the overall sense of wellbeing. Many types of enrichment can include this element of seeking.  

So, in the sixth and final article, we will be looking at some of the main types of enrichment, to bring the series to a very practical end.  

© Alison Campbell, 2020 



Affective Neuroscience – The Foundations of Human and Animal Emotions – Jaak Panksepp (Oxford University Press) 

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5411330/ - Effect of fasting on health and disease.  

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4450283/ - Mastication as a stress coping behaviour.