fei75766_ch14_435-462.indd 456  02/06/20 01:10 PM
Part V    Biological/Evolutionary Theories456
researchers havebegun touncover specific genelocations involved inproducing neu-
rotransmitters, suchasserotonin, thatareconnected totraits ofextraversion, neuroti -
cism, andpsychoticism (Gillespie etal.,2008).
Insummary, research tends tosupport Eysenck’s notion thatpersonality fac-
torshaveabiological basis andarenotsimply dependent onwhat wehavelearned. 
Indeed, consistent withabiological basis ofpersonality, themajor traits appear tobe
consistent inmost countries oftheworld (McCrae, 2002; Poortinga, VandeVijver, 
&vanHemert, 2002). How andwhen personality traits areexpressed isclearly influ-
enced byourcultural andsocial context. Butthatweallcanbedescribed onsimilar 
dimensions ofpersonality (e.g., extraversion orneuroticism) isinfluenced byourbio-
logical makeup. Personality, inshort, ismolded bybothnature andnurture.
The Biological Basis of Neuroticism
Recall thatEysenck (1967) postulated thatneuroticism resulted from increased activ-
ityorresponsiveness andlower activation thresholds inthelimbic system. Thispattern 
isthesame asintroversion butthelocation isdifferent: introversion involves increased 
activity andlower thresholds forcortical andreticular arousal rather thanlimbic sys-
temarousal. Thelimbic system iscomprised ofthesubcortical structures inthebrain 
involved inemotion andmotivation, primarily theamygdala andhypothalamus. There -
fore,researchers haveexplored Eysenck’s hypothesis thatdifferences inlimbic system 
activity andphysiology arethebasis forneuroticism—the disposition toexperience 
negative emotions suchasstress, anxiety, guilt, anddepression. Ingeneral, there is
quite abitofempirical evidence supporting thistheory (Mitchell &Kumari, 2016).
Forinstance, Mincic (2015) conducted ameta-analysis onthetopic ofneuroti -
cismandthestructure andfunction oftheamygdala. Meta-analyses aretheprocess of
collecting allofthepublished andevenasmuch unpublished literature asonecanfind
ononespecific topic orquestion andcalculating theoverall sizeoftheeffect ontheques-
tionathand. Itisaquantitative review oftheliterature andtellsushowlargeofaneffect 
there isacross allstudies rather thanjustone.Mincic collected andanalyzed 13quanti -
tative studies onbrain structure andfunction andneuroticism. Across these 13studies, 
there wasconsistent evidence formore greymatter (cellbodies) intheamygdala of
people highinneuroticism compared tothose whowerelowinneuroticism. More grey
matter isconsistent withincreased activity orresponsiveness oftheamygdala. Tobefair,
thisassociation isnottrueforeachamygdala. Likeallsubcortical structures ,theamyg -
dalacome sintwos: oneintherighthemisphere andoneintheleft.Increased amygdala 
activity isfound more intheleftthanrightamygdala (Mincic, 2015). Other research sug-
geststhatthere arereduced neural connections between theamygdala andother brain 
regions involved incontrolling thoughts. Thislackofconnection appears toinhibit the
“offswitch” intheamygdala ,resulting initsoveractivity tonegative experiences (Canli, 
2008; Ormel etal.,2012). Inshort, people highinneuroticism arebiased toward and
more sensitive tonegative emotional experiences partly duetoanoveractive amygdala.
Increased physiological reactivity—as seeninsweating—is alsoassociated with
neuroticism. Inonestudy, forexample, 169adults (mean ageof27)hadtheirphysio -
logical responses measured astheywatched a60-minute TVprogram (House )(Brum -
baugh, Kothuri, Marci, Siefert, &Pfaff, 2013). ThisTVepisode waschosen because it
included fourseparate 1-minute scenes thathavebeen demonstrated toportray strong Final PDF to printer