Neuroscience & Brain Mechanisms Of Critical Periods In Puppy Development. This Should Be Started Before You Get Him Home.

The most critical period for puppy development is the age six to eight weeks (everything that happens prior to this is to do with setting the foundations of the animal & why it is essential that you have chosen a good breeder).

Most puppies leave their litter around 7-12 weeks to go to their new home (in the UK this is sometimes 6-7 weeks). This first week is absolutely crucial and is the week before they get their second lot of jabs. In this first week our window of opportunity (neuroplasticity, axonal formation, synaptic plasticity) is starting to close, so it is essential that we are quick to set up this young brain to succeed. This article looks at what is going on from a neurobiological (neuroscience, genetic, microbiological, chemical, biological) perspective and why timing and getting it right are so important.

Our 7 Day Puppy Survival Guide (owner/enthusiast/professional) schedules, downloads, step-by-step videos on training, habituation, socialising, play, potty training, prevention of separation problems, etc. It covers a different task each day. At the end you get a certificate to prove you have survived the first 7 days of owning a puppy.

Some of the schedules & information in the 7 day series (these form part of the essential resource guide):

The course is fully view-able on any android device, fun for the whole family and the interactive sheets are easy to follow, fun and useful to help you monitor your progress. It really is all you need to set your dog on the right road for his life with you, before you take him to training classes. Please do not let your puppy become another statistic. It may just be the best £9 you ever spend, go to: 7 Day Puppy Survival Guide (owner/enthusiast/professional)

Why is this so important?

When a puppy (any animal) is born, the brain is changing in accordance with the sensory experiences that the animal gains. By sensory we mean sight, hearing, touch, licking, grooming, affection etc. Before the eyes even open, the pups use their sense of touch and smell to detect where Mum is for feeding, warmth etc. This critical bonding-nurturing stage is an essential foundation for the emotional set-point of the animal. Our puppy instructor course covers this in a little more detail (a 10 week course covering everything to run a successful puppy class, go to: Puppy Training Classes Instructor Course. The following article briefly highlights the critical period for somatosensory development: Somatosensory Development, The Psychobiological Substrates Of Attachment & Learning In The Critical Period.

During the critical stages, the functional and structural connections of neurons in the cortex of the brain are particularly susceptible to alterations. The time course, for experience mediated sensory development, is very much dependent on which system we are considering. Studies of rats reared outside, compared with those in a cage have shown that they have much larger brains and higher levels of cognitive function.

If you deprive an animal of sensory experiences, the brain rewires, allowing the deprived cortex to process inputs, from less deprived senses in a process of cross modal plasticity. This helps the animal to increase performance in the remaining senses when one is deprived.

What does this mean?

Basically, the brain will compensate in some way for the lack of appropriate wiring to adapt with the skills that it does have. What are the implications behaviourally for this?

Environmental Experiences involving experience around touch, handling, sound, movement, light, dark, texture, motor activity and play help the brain grow connections to help the organism to interact with his environment. The brain literally grows each time the organism adapts.

What happens if we do not adapt our puppy? 

Failure to adapt your puppy to sounds, surfaces, noises, people and novel objects (please download our habituation schedule in our Essential Training Resource Guide) means that he will be less able to cope emotionally and physiologically with the world. These early experiences will enable him to become more resilient please see the following articles: The Relationship Between Stress, Aggression & Resilience & Neural Mechanisms Of Resilience & Its Role In Dog Training

Puppies who do not have these early experiences in these critical stages, have a less developed axonal, dendritic and synaptic connection pattern in their neural circuitry. i.e. his brain will have less connected wires, which represent the different functional networks (connectomes) of his brain.

Without these early experiences, he will be less able to deal with the experience that mediates the tuning of his sensory system surrounding excitation and inhibition (he will be easily excited and aroused which means he is less able to deal with variations in his daily activity). The hormone response elements (HRE’s) actually inhibit the ability for the animal to learn new things. This is because they inhibit the transcription factors that are fundamental to DNA replication processes and the formation of new learning experiences. This lack of environmental adaptation renders him incapable of dealing with environmental stressors. If learning happens in this critical stage, when we have neuroplasticity, it is far more likely to help him deal with novel situations when he is older. Please note: any exposure to a new object has to be paired with a positive experience in some way. If the experience is traumatic, you might just be setting him up in this stage to generalise fear. This is why you need a solid habituation schedule and enrichment learning activities. Any breeder will have already set the wheels in motion with this and this first week (depending on where you are from globally depends on what week you will get your puppy) is vital to helping him learn new experiences. Check out the following link, every single breeder should be part of this: Puppy Culture

A map of each sensory function is set out in the somatic sensory cortex (an area in the brain cortical region) and it will have a topographic representation in the way the cortex is organised (each experience is physically represented as a group of interconnected neurons). This map is established in the critical period. So, for example, animals with whiskers will have a topographical map representing each whisker and each map will contain the tactile information necessary for this function. This starts to form in the first week post-birth and it precedes the visual & auditory critical periods.

Studies show that the effects of odour and auditory development share similar organisational constructs as the somatic sensory systems and that, deprivation of olfaction reduces the organisation of the brain’s networks (astroglial networks).

There are many studies showing the effects that environmental enrichment (EE) has on animals. Some of these studies date back as far as 1947. For example, Donald Hebb took rats home and cared for them as pets. He found they performed much better on problem-solving tests than those raised in cages. This spurred further research into how we can enrich the life of caged animals because, by adding bigger cages, toys, colours, shapes, tunnels, materials, nests, shelters, ladders, wheels, social interaction (a greater number of other animals to interact with), larger cages  (more space) and exercise opportunities. These all have the function to induce brain changes from a cellular, molecular and genetic level. The brain actually gets heavier and bigger. The buck does not stop here, by making these changes and helping the animals adapt in this way to their environment we are actually altering their DNA and these small changes each time will be passed down generations. You only have to look at the studies being carried out on Foxes to gain some insight to the effects of domestication on animals. Particularly our dogs, please see the following article Evolution Domestication & Cognition- The Biology Of Dogs

Not only does the brain get heavier, there is an increase in hippocampal neurogenesis. The hippocampus is the area of the brain associated with learning. The term for learning is neurogenesis. Basically,  when there is enrichment, there are more connections between neurons, more branching of dendrites and synaptic size increases in the brain. This is particularly relevant in the visual cortex.

Below schematic of a typical axon, nerve cell, dendrite

Raising an animal in an EE (enriching environment) not only improves memory and cognitive processes, it increases exploratory activity (a sign of a more securely attached animal, emotionally, see the following article Attachment, Development and Emotion- A Neurobiological Perspective and any studies by Bowlby who talked alot about attachment. When there is secure attachment there is less anxiety and an ability to deal with novel stimuli. There is also less neophobia and an increased ability to deal with traumatic insults later in life. It shapes the brain and gives the animal more tools to cope to survive.

The critical time course during experience-mediated brain development is a unique event. The closure of this critical period is complete when the anatomical and functional phenomena are established. There are special nets that form around the neurons and then myelin related proteins inhibit axonal sprouting (the critical period of neuroplasticity ceases). This end of critical period is modulated by the functional changes in the activity of the neurotransmitter GABA (gamma amino butyric acid) and its specific receptors in the cortex.

What are Neurotransmitters?
They are chemical molecules that are used by the brain to allow nerve cells to communicate with each other. They convey chemical messages which give rise to behaviour and physiological outputs depending on intrinsic, genetic and learned factors pertaining to the perceived environment, both internally and externally. Their growth, action and specificity are very much shaped by early enriching experiences during this critical period. This is a complex area of neurochemistry and some of the specifics in terms of cell signalling are still very much at the discovery stage. Please see the following 2 seminars which go into more detail on the research into the neuroscience of behaviour  Introduction To the Science Of Behaviour (Beginners) Seminar &  Introduction To the Neuroscience of Behaviour On-line Seminar (Degree level)

There are many neurotransmitters that each have differing effects. The main ones that you will come across are: Dopamine, Serotonin, Noradrenaline and for the purposes of neuroplasticity and critical periods, it seemed pertinent to mention the neurotransmitter- GABA.

Common neurotransmitters and their functions in animals:

gaba dopamine gaba actions

Dopamine, Noradrenaline & Serotonin are all Neurotransmitters responsible for specific behaviours relating to an excitatory, inhibitory and neuromodulatory perspective. We go into this in a lot more detail in the seminars.

The neurotransimitter we are interested in when discussing neuroplasticity (neural growth and development) is GABA (gamma amino butyric acid). This is an inhibitory neurotransmitter. When it docks at a receptor site, it reduces the activity of that neuron and makes it less likely to fire (termed action potential). This happens because GABA controls the admission of negative chloride ions into the neurons and potassium ions out of them. This influx of negative charge increases positive charge outside the neuron and then it is difficult for the action potential to have its effect on the adjoining neurons (so the electrical and chemical message does not travel). This is particularly useful when it is involved in processes that reduce neural activity such as anxiety, calming and releasing tension/stress.

So, what?
Anyone who watched the recent lecture, on the introduction to the neuroscience of behaviour Introduction To the Science Of Behaviour (Beginners) Seminar or Introduction To the Neuroscience of Behaviour On-line Seminar (Degree level), would have understood the role that the vagus nerve has in neurogenesis due to its relationship with the parasympathetic nervous system.

When the sympathetic nervous system is engaged (the system that gives us the stress type responses when we perceive threat) it inhibits a number of factors, one of which is neurogenesis (no learning when you are stressed). Basically, when the vagus nerve is tense, so are you. It is only when this is relaxed that you have parasympathetic control and a relaxed body that is primed for learning.

The cardiac vagal neurons (CVNs) moderate and slow heart rate & keep it from becoming too rapid. GABA has an inhibitory effect upon these neurons. It keeps the body alert, in rhythm, reduces anxiety and it primes the body for learning. It is synthesised from Glutamate (an amino acid and also a neurotransmitter), vitamin B6 and other amino acids. Researchers have shown that GABA is responsible for the onset of critical periods. Suppressing this production in a visual cortex of a mouse leads to complete blindness if it done at the critcal stage.

I hope this article helps to show how our early experiences can affect the brain from a scientific point of view. It is important to note, that whilst genetic factors determine the initial sequence/levels of genetic neuronal activity, this information can be modified as a result of experience that takes place during the critical developmental periods. This is huge, because it governs behaviour, physiology, susceptibility to disease and many other factors. Using applied techniques we can work to modify behaviour by considering their functions and providing preferable more reinforced desirable behaviour outcomes for animals. Please see case studies Case Study Using ABA On Resource Guarding Between Two DogsFunctional Assessment Using ABA To Treat Recall Problem In Dogs

and an aritcle which gives you The Solution To Most Dog Behaviour Problems

The most important primary foundation, in this process, is maternal care. This helps to shape the animals emotional set-point, priming him neurobiologically to be more resilient experientially to neuroendocrine stress responses, depression and anxiety related situations.

The area of the brain that we frequently measure when considering the emotional set-point is called the HPA (hypothalamic pituitary axis). This brain area that is measured to gauge responses to fearful or threatening situations. It is how the HPA engages with the pre-frontal cortex (the executive function part of the brain) that will determine the way the animal will engage with his environment. Without this type of early experience/habituation you are more likely to have amygdala hijacking (primitive responses). We want to prime the animal to consult his pre-frontal cortex and make more measured and considered behaviours without engaging his primitive hindbrain This can be  mentally, physiologically and emotionally expensive for the animal. We do not want him living in fear basically!

We have developed the Essential Training Resource Guide To Help Behaviour Professionals Raise Awareness Through Interactive Posters & Schedules (please note the IAABC posters are free with this pack and developed by Lili Chin)- See Gallery Below:


Exposure to potential stressors such as cold and separation leads to an enhanced HPA activity and when this is experienced in the critical period, animals are far more likely to be resilient to the stressful effects of this. The knock on effect of handling, early separation and maternal care leads to an increased cognitive and emotional health throughout life. Plasma cortisol levels have been found to be lower in rats handled early in life, compared to those not handled. Rats handled in infancy seem to be endowed with improved differential responses to varying intensities of stressful stimuli. They perceive and respond to mild challenging stimuli that are associated with improved cognitive function, yet recover more rapidly, from strong stressors that might have adverse effects on neuronal function. it is also found that animals suffering from depression have an enhanced activation of the HPA axis and this is expressed in the cortisol, mRNA (messenger ribonucleic acid- this is copied from DNA when proteins are about to be made in the cell) and protein level within the animal.

Adequate licking and nursing care in pups causes gene expression, that reflects in adequate concentrations of hormones and neurochemicals to enable more resilience to stressors later in life (licking and nurturing turns on the hormones in  glucocorticoid system). Genes and the environment converge powerfully during early sensitive windows of brain development to form the neural circuits underlying behaviour.

During these early periods, the developing nervous system must obtain certain critical experiences, fulfilling their sensory, physical, or emotional obligations. This enables the animal to mature properly. During these periods the internal environment is such that, the animal is optimally primed for high rates of learning, as well as the ideal consequences available for neuronal connectivity.

After the critical period, connections diminish in number and are less subject to change, but the ones that remain are stronger, more reliable, and more precise. These turn into the unique variety of sensory, motor, or cognitive “maps” that best reflect our world. It is important to note, that there are multiple critical periods throughout an organism’s life. These are organized sequentially, as individual brain functions are established. Thus, even the brain of an adolescent is not completely mature.

Injury or deprivation of environmental input occurring at specific stages of postnatal life, dramatically reshape the underlying circuit development, which becomes increasingly more difficult to alter later in life. The term often used is: “use it or lose it.” So, in order to make sure you are giving your pup everything he needs, to be primed, for this complex world (that we are imposing on him) you need to make sure you fulfill your obligation to him straight away. Work through the habituation schedule. Complete our 7 day survival guides, buy him the best toys, products, give him the best experiences and above and beyond anything, touch, handle and love him in a positive way.

Further Useful Articles:

Please note, all of our courses are certificated and gain you CEU’s.

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Hypothalamic-pituitary-adrenal (HPA) axis Plotsky, & Nemeroff, 2004).

Experimental animals including rodents (Hess, 1969; Levine & Lewis, 1959; Meaney et al., 1996)

Primates (Levine, 1993a; Heim, Owens, Plotsky, & Nemeroff, 1997).

HPA axis and the hormonal responses to stress during adulthood (Brunson, Avishai-Eliner, Hatalski, & Baram, 2001; Levine, 2000).

The set-point and magnitude of the responses to stress are under tight and intricate regulation (Joels & Baram, 2009; Walker & Dallman, 1993)

Hippocampal glucocorticoid receptors (GR) and hypothalamic corticotropin releasing hormone (CRH)(Heinrichs, Menzaghi, Merlo, Britton, & Koob, 1995; Rivier & Vale, 1983)

These hormones interact with GRs in hippocampus, PVN, prefrontal cortex, and pituitary (Peiffer, Lapointe, & Barden, 1991; Spencer, Miller, Stein, & McEwen, 1991; Swanson & Simmons, 1989)

Exposure of neonatal rats to age-appropriate physiological and psychological stressors such as cold (Yi & Baram, 1994)

David Hubel and Torsten Wiesel 1960s, How does the brain develop if vision is temporarily blocked?

 Authors Biography


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