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U of T study shows infants can remember emotional events

August 25, 2010

TORONTO, ON — A new study led by a Uni­ver­si­ty of Toron­to Scar­bor­ough psy­chol­o­gist shows that human infants can remem­ber unusu­al emo­tion­al events.

Inves­ti­gat­ing the impact of rela­tion­ship dis­rup­tions on stress reg­u­la­tion in infants, researchers asked par­ents to briefly ignore their six-month-old infants dur­ing an exper­i­ment, which caused an ele­va­tion in infant stress hor­mones, said Dr. David Haley, a psy­chol­o­gist at the Uni­ver­si­ty of Toron­to Scar­bor­ough and the lead inves­ti­ga­tor of the study.

To see whether infants would remem­ber this episode of parental unre­spon­sive­ness, infants were re-exposed to the same con­text after 24 hours. Although par­ents did not ignore their infants on this sec­ond day of the exper­i­ment, the infants demon­strat­ed an antic­i­pa­to­ry stress response, as evi­denced by an ele­va­tion in cor­ti­sol, a stress hor­mone. Over­all lev­els of stress hor­mones were low­er on the sec­ond day com­pared to the first day, how­ev­er, sug­gest­ing that infants can antic­i­pate the stress­ful event based on expec­ta­tions about how their par­ents will treat them, but are able to adapt to the stres­sor.

“The capac­i­ty to adapt to changes in par­ent­ing may be an evo­lu­tion­ary advan­tage that con­tributes to the rec­i­p­ro­cal nature of the par­ent-infant rela­tion­ship in humans,” said Dr. Haley.

The results of the study are pub­lished on August 25, 2010, in The Roy­al Soci­ety jour­nal Biol­o­gy Let­ters.

“What the new data make clear,” said Jay Bel­sky, Direc­tor of the Insti­tute for the Study of Chil­dren, Fam­i­lies and Social Issues at Bir­beck Uni­ver­si­ty of Lon­don, “is that the infant does, indeed, remem­ber in some man­ner how stress­ful life is and, in line with attach­ment the­o­ry, devel­ops expec­ta­tions about the future.”

Clyde Hertz­man, Direc­tor of the Human Ear­ly Learn­ing Part­ner­ship (HELP) at the Uni­ver­si­ty of British Colum­bia, said the research helps explain the bio­log­i­cal basis of bond­ing and attach­ment because it shows that chil­dren as young as six months have the capac­i­ty to remem­ber stress­ful events in inti­mate con­texts.

“Most impor­tant, it helps us to under­stand why social and emo­tion­al depri­va­tion in the first year of life can have pro­found long-term impacts on child devel­op­ment and men­tal health,” said Hertz­man.

Dr. Haley said researchers are only begin­ing to under­stand the basic mech­a­nisms that enable human infants to antic­i­pate, remem­ber, and adapt to unusu­al emo­tion­al events in an attach­ment con­text. It remains unknown whether the mem­o­ries that trig­ger the antic­i­pa­to­ry stress response are locat­ed in the mind or body.

“It isn’t clear where or how the infor­ma­tion is being retained,” said Megan Gun­nar, Pro­fes­sor of Psy­chol­o­gy of the Insti­tute of Child Devel­op­ment at the Uni­ver­si­ty of Min­neso­ta. Rather than sug­gest­ing that “the child can ‘think’ about yes­ter­day,” she said, “I might shift more to the wis­dom of the body (the child’s stress sys­tem retains the expe­ri­ence).”

The study also sug­gest­ed that behav­iour­al and phys­i­o­log­i­cal com­po­nents of the stress sys­tem are loose­ly cou­pled. Dr. Haley said that each com­po­nent of the stress sys­tem “may adapt accord­ing to dif­fer­ent sched­ules.

“The mem­o­ries that acti­vate each com­po­nent of the antic­i­pa­to­ry stress response may not be in sync, and spe­cif­ic mem­o­ry cues may be need­ed to acti­vate each com­po­nent of the stress response. For exam­ple, the infant might have to sit in the chair again before his or her neg­a­tive affect increas­es, where­as sim­ply see­ing the chair caus­es the release of stress hor­mones.”

Dr. Haley is con­duct­ing fur­ther stud­ies on the per­sis­tence and sta­bil­i­ty of the infant antic­i­pa­to­ry stress response.


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