Human beings are the only primates where the birth canal is smaller than the head. Therefore birth is going to be a traumatic event. (Even caesarean sections mean a child being taken from the warm secure womb before the birth is triggered in the mother and baby.)

In the core part of the babies brain, where the functioning of the body is controlled, there are two ways of responding to such an event.
The first raises bodily functions and readies for action (fight or flight).
The second slows down bodily functioning and action becomes less likely.

If the birth is difficult because the mother is holding on (for what ever reason) then the child fights to get out as it is in danger of dying.
If the birth is dangerous, (i.e. because of a strangling cord) then the child becomes passive to protect itself.
The choice of reaction to this initial trauma is imprinted on the core brain and will determine any initial response to danger or new situations later in life.

(Based on the work of Arthur Janov)

Our personality and behaviour traits are determined by our early childhood experiences.

A Child is born into this world open, vulnerable and dependant. That child has built in needs or drives to achieve survival and flourish but those needs are to be provided for by its parents. The child's needs are for food, protection and comfort. The internal mechanism that promotes that is the pleasure /pain principle. If the child gets these needs met it feels pleasure within itself and towards it's parents. If the child does not get them met it feels pain as a stimulus to put things right, often by crying which its parents are programmed to respond to. If the child does not get those needs met on a consistent basis it will automatically adopt a strategy to deal with the ongoing painful situation. The exact plan will be determined by the way it's parents fail to provide for it's needs. That strategy will become hard wired into it's psyche so as to stop it feeling the unrelenting pain of unmet need. This strategy will either be a means of suppressing internal feelings or away of eliciting from parents some compensatory behaviour towards it to alleviate the pain. These hard wired reactions and behaviour then becomes the basis for its personality and is the creation of its inner child

The type of parental failure determines the age of the child at which this will have the most marked effect. The brains development will then determine how the child will experience this.
There are three levels to the brain and these exist in different physical parts of the skull
The core level operates all the unconscious bodily functions. (-0mths) ‐ Sensations
The second level feels and processes the emotions. (+6mths)
The third thinks about how to get needs met and provide rationalisations for set patterns of behaviour established by other levels. (+1yr)
The basic core brain needs are for food, protection, and comfort.
When the emotion brain starts to develop then these basic needs will start to be expressed in emotional terms such as affection, attention and interest without which the child will feel insecure and unsafe
The thinking brain will expect the parents behaviour to be consistent with basic or emotional needs and if they are not the child will feel unsafe and unprotected and unwanted.

(Based on the work of Arthur Janov)

Authur Janov became famous in 1970s with the publication of " The Primal Scream ". While working as a Clinical psychologists exploring deep childhood trauma a patient started to emit a cry from deep inside. This led to a theory that all seemingly intractable psychological problems stemmed from repression of feelings associated to childhood trauma. The techniques he developed called Primal Therapy tried to help people access those feeling by regressing to childhood states supported by a therapist. An updated version called " The New Primal Scream" mostly rewrites the section on homosexuality, no longer regarding it as psychological issue to be solved.

The establishment of psychology and psychiatry within the health services has meant that the power for making judgments about valid treatments lies with a profession dominated by the drug companies where a physical cure means great profits for them. Consequently drugs for depression are handed out like sweets by general practitioners trained in physical diseases even though these drugs have little effect other than to cause dependency. Non medical approaches are dismissed out of hand by doctors paid money by drug companies to do so. If you read an article on Arthur Janov you must expect a phrase like " now dismissed as unscientific and ineffective ". Primal therapy is best judged by those who have ventured there. It requires a courage to go beyond our psychological blockages to find what lies there and cannot be judged by those who fear to tread and don't want others to be free. My view is that his basic theories are correct and those childhood traumatic states are there waiting to be accessed. They are held in our innerchild and if we don't release these feelings that innerchild will act unconsciously or consciously to disrupt our lives.