Table 1.

Main features of candidate gene carriers in relation to positive memory.

Candidate Genes	Main Role	Relationships with Positive Memory
ADRA2B (209 bp/200 bp)	Regulation of neurotransmitter release from sympathetic nerves and adrenergic neurons in the CNS	Deletion (200 bp) carriers show enhanced emotional stimuli processing and memory
		Deletion carriers have higher cognitive–affective flexibility compared with non-carriers
		Deletion carriers preserve emotional faces’ recognition abilities under acute stress conditions
COMT (Val158/Met158)	Metabolism of catecholamines and l-dopa	Met158 polymorphism is linked to increased neural activation for negative stimuli Met158 allele carriers have reduced performance in emotion-related tasks
		Met carriers have better WM performance, while Val carriers are better in processing negative stimuli
5HTTLPR (S/S; L/L; S/L genotypes)	The serotonin transporter (5-HTT) gene mediates the serotonin reuptake from the intersynaptic space	S-allele carriers show decreased left fusiform gyrus activation to positive stimuli
		S-allele carriers experience greater emotional responses to negative stimuli than l-carriers
		L-allele carriers are more efficient in emotion regulation than s-carriers
CB1 (AA/AG/GG genotypes)	Modulate neurotransmission by inhibiting presynaptic Ca	Carriers of at least one copy of the minor A allele show improved consolidation for emotional events into autobiographical memory than GG genotype’s subjects
		Carriers of the combination of CB1 and ADRA2B polymorphisms show enhanced memory and a positive effect bias
		One copy of the minor A allele could be a protective factor against depression after stressful events
TOMM40 (intron 6: S/L/VL; intron 2: AA/GA/GG)	Allows protein import from the cytoplasm into mitochondria	S variant of intron6 is associated with enhanced memory performance and executive functions
		AA genotype shows a positive memory bias compared with G-allele carriers