mice with lesch - nyhan syndrome interpret all information as aggression , to which they respond by defensive aggression . in this x - chromosome
 linked recessive syndrome , there is a deficiency of the enzyme hypoxanthlne guanine phosphorlbosyl transferase ( hprt ) , which does not degrade uric acid properly . in these conditions ,
the basal ganglia and the amygdala can be permanently activated by too much uric acid , an otherwise useful antioxidant .
this is a clear instance of a mood disturbance being induced by an endogenous substance .
another chromosomal abnormality , down 's syndrome , which is common in monkeys , induces a very different development , where the affected animal is easygoing and behaves like a  superbaby .
the first example , among many others , reminds us how mood states are sometimes massively shaped by the biology of the brain , independently of the environment .
however , the example below illustrates how the environment interacts with the genes . in his paradigmatic protocol from the early 1960s ,
harlow used partial or total sensory deprivation and showed that this induced severe developmental disturbances .
eight very young rhesus monkeys were separated from their mother and raised in isolation in cages containing two surrogate mothers : one made of wire incorporating a nipple that gave milk ; the other covered in terry cloth with no nipple , thus giving no milk . at each stress , in the form of mechanical teddy bear beating a drum , the baby monkeys were startled and leapt for reassurance onto the terry - cloth mother .
as soon as they made contact with this secure base , the monkeys lost their anxiety .
but , in the absence of the terry - cloth mother , they would run in every direction , whimper , and stop eating or sleeping . in summary , they were soothed by contact with the soft mother surrogate and panicstricken in its absence . 
 
although most baby rhesus monkeys are impaired in their development , some even fatally , a few pursue their growth as if they had no need of the secure base of a mother .
monkeys with the short form of the 5-hydroxytryptamine ( serotonin , 5-ht ) transporter ( 5-htt ) gene appear less able to cope with inadequate mothering .
those with the long form of the 5-htt allele , on the other hand , do not experience the inadequate mothering as a deprivation or as a cause for anxiety , and they continue their normal development .
the long form of the 5-htt allele leads to the synthesis of more 5-ht in the synapses and interstitial fluid .
these observations are synchronic , meaning that they refer to a single point in time .
the same maternal falling plunges the baby monkey with the short form of the 5-htt allele into mood disturbances , but the baby monkey with the long form of the 5-htt allele will not experience the same information as a loss .
i perceive defective mothering that impairs my mood ,  would say one baby monkey ; while another would say  i perceive the same defective mothering , but it makes me seek out a sensory surrogate in my environment to maintain my peace of mind .  the changes in physiological regulation ( homeostasis ) that occur with mood changes
this diachronlc dimension reveals that , through repetition of a given interpretation of the sensory information , the monkey with the short form of the 5-htt allele eventually develops a distinctive style of existence .
every encounter involves trauma and this monkey avoids socializing play and experiences all unexpected information as an alarm , often responding by fight or flight ; its path in life is littered with emotional alerts , dazed mood , and interaction difficulties . 
 
thus , when a vulnerable baby monkey is raised by a competent mother , it acquires a style of attachment that is secure , calm , and confident . an environment with stable developmental tutors enables it to mature in security with a decline in vulnerability . on the other hand , a baby monkey with the long form of the 5-htt allele , although less vulnerable to emotional loss , may have developmental difficulties in an overstable environment .
a female rat stressed during the last part of pregnancy will give birth to a litter with durable increased biological correlates of stress , such as enhanced cortlcosterone secretion . 
 
all these results from studies in observational and experimental ethology suggest that the same genetic pattern can produce emotional vulnerability in an unstable setting or emotional strength in a stable setting .
this model can also be applied to the development of children . at the embryonic stage ,
as its memory develops , the baby manifests habituation in the cognitive sense of the term , in that it decreases its response to tactile or auditory inputs that have become familiar through repetition .
the emergence of memory has made it possible for a present perception to be modified byor aftercomparison with a similar perception from the past .
absence of appropriate sensory stimulation during this stage of intense fetal neuronal and synaptic development could impair the organization of information circuits .
after birth and during the first years of life , this could lead to a failure to give a form to the perceived world , and to the fact that all information is flagged with an alert status because it does not fit into a circuit that would permit an appropriate response .
all information , even if purely physiological , thus becomes a stressor . in 1946 ,
clinical neurologists observed a very high frequency of frontal lobe and limbic system atrophy in the gas encephalograms of holocaust survivors , which they explained by a vitamin deficiency according to the scientific myth prevailing at the time .
after the fall of the iron curtain in 1989 , computed tomography scans of romanian orphans institutionalized under catastrophic conditions of sensory deprivation demonstrated the same frontal lobe and limbic system atrophy . on this occasion , however , the prevailing scientific interpretation took ethology into account , and this sometimes massive cerebral atrophy was attributed to sensory deprivation . 
 
modern neurobiology can now describe stages and conditions of nervous system development where given stimuli can result in atrophy , normality , or repair .
to take the example of light - deprived kittens , sensory deprivation abolishes traffic across physiological synaptic pathways .
not only does the corresponding brain area then fail to develop the dendrites that would normally have filled their allotted space , but also any subsequent visual physiological stimulus and information will be interpreted as a stress . with functional imaging techniques ,
one observes that these light - deprived kittens , when later exposed to visual stimuli , have a profusion of occipital neuron activation , despite failing to process the visual information properly in contrast , when a neuronal circuit has been adequately trained by the repetition of normal sensory stimulation , it can handle information at a lower energy cost , le , neurons are not overly activated .
emotional deprivation might have toxic effects on brain development that make the individual more or less incapable of processing emotional information .
even the banal and everyday fact of being touched by another person or a simple glance or word unleashes aggression .
affected children bite themselves when somebody smiles at them or bang their head on the floor when somebody looks at them .
the interpretation of these sensory stimuli as being threats to oneself is accompanied by an increase in secretion of glucocorticoids .
this might lead to neuronal damage and death , in particular in the pyramidal cells of the ca3 area in the hippocampus . during the early phases of the dazzlingly fast development of the brain ,
external information can participate in dendrite formation : an environment of sensory impoverishment substantially decreases brain mass in the area of the hippocampus .
a large number of other factors also influence brain maturation . some of these factors are physical , such as the secretion of hormones .
for example in 1057 people followed from birth to the age of 26 years , neither life stress nor the polymorphism of the 5-htt alone was able to predict the occurrence of a major depressive episode .
however , the combination of a high load in life stressors and having the short form of the 5-htt allele did serve as a predictor . stress had no influence on people who had the long form of the 5-htt allele .
this suggests that the 5-htt polymorphism determines the  taste  of the world for the individual as well as temperamental dispositions , such as harm avoidance .
other factors are social and cultural , for example , the beliefs or myths about how to best take care of newborn babies and children .
imprinting is a process readily observed in nature and equally readily demonstrated in the laboratory .
it differs from other forms of learning by becoming established with great rapidity at a very early stage in development . at a particular time and
a sensitive stage in its growth , the body becomes highly sensitive to all external information reaching it . in this way ,
auditory , olfactory , or visual objects become imprinted in memory , in the limbic system , sensitizing the individual preferentially to a type of information . from then on , it is with heightened sensitivity that the individual perceives a particular maternal body languageor a song , intonation , landscape , or smellbecause this sensory object for the individual stands out from all others . from this stage of development onwards ,
the individual 's world is categorized into hyperfamillar imprinted objects , which induce a feeling of security that allows him or her to explore the environment and hence lead to other forms of learning . by contrast , in a world deprived of imprinted objects , the individual experiences all information as aggression .
he or she responds with alert reactions ( discharge of catecholamines and cortisol ; cerebral arousal ) and disorganized fight or flight behavior .
the plasticity of the human nervous system , the length of its development , makes it impossible to speak of imprinting in humans .
this does not exclude astonishing receptivity in the early years and a huge potential for rapid learning .
moreover , an apparently identical external fact could have completely different effects , depending on the development stage and the memories already acquired . although one can not talk of imprinting in the sense of the early and automatic affiliation that was studied by konrad lorenz
these phases , together with the keen memory of humans , explain why early interaction could mold temperaments , through incorporation into implicit memory of preferential sensitivity ( the  taste  of perception ) and relationship skill ( the style of attachment ) .
the imprinting of sensory objects thus tailors the nervous system to perceive a particular type of world , select certain items of information , and create a personal representation of oneself interacting with others .
 several lines of research show that the experiences and the environment encountered during critical periods of development can lead to long - term changes in the expression of the genome .
for example , female rats who lick their newborn offspring more often during the first week of life induce in them a lesser responsivity to stressors , lasting into adulthood .
these behavioral changes are accompanied by a higher number of glucocorticoid receptors in the hippocampus due to an epigenetlc modification of a transcription factor of this receptor . 

the above facts could induce resignation (  we are the puppets of our genes and environment ; we are molded by our experiences  ) , were there not the option of reworking our representation through speech .
how we talk about our past , and the stories we tell ourselves about our present and our future , reflect our feelings and emotions
. the same facts can induce different feelings because each person has a different history , and does not attribute the same emotion to the same verbal representation .
the fact that the emotional response to the same story differs between listeners invites the speaker to make the effort of empathy , by which he or she looks at himself or herself from the outside .
this use of speechthis rhetoricexpresses the emotions of the inner world , organizes the behavioral consequences of these emotions , and thus explains the possibility of mental transmission . between molecular biology on the one hand and emotion - structuring speech on the other
, mood stands at a confluence of determinants , and is subject to modification by each .
 the insights of ethologythe science of animal behavior from a biological and psychological point of viewwere incorporated in the 1950s by the british developmental psychiatrist , john bowlby , into his attachment theory which argued that a secure affective base in infancy was critical to the normal development of perception , cognition , learning , and emotion , in addition to that of physical parameters . 
 the theory was illustrated by harlow 's pioneering experiments with baby monkeys : those raised with a wire - frame  mother  failed to thrive , compared with the more normal development of those deriving comfort contact from a terry - cloth surrogate . 
 modern neuroscience techniques have confirmed that the absence of sensory stimulation during periods of maximal synaptic expansion provides the substrate for a subsequent mood disorder , ethology offers a novel  nature plus nurture  approach to the development of abnormal mood , as well as a target for treatment . 
Animal ontogenesis
Human ontogenesis
Memory traces
Feelings and words