Gender differences evident on functional imaging in the partner preference and early phases of love warrant mention. However, social attachment does occur even in the absence of gonadal steroids suggesting that gonadal hormones are only a small piece of an intricately knit puzzle that form the complex phenomenon called love. Gonadal hormones may further regulate OT and vasopressin through indirect mechanisms. Testosterone further enhances vasopressin levels in the medial amygdala lateral hypothalamus and pre-optical medial area which are involved in aggressive behaviors. Testosterone through these receptors may suppress levels or activity of serotonin which apparently increases aggressiveness. Testosterone receptors are distributed in the hypothalamus. Sex hormones may exert developmental effects on neural systems involved in social attachments and may mediate both genetic and environmental influences on the propensity to love and form attachments. The role of gonadal hormones in this regard appears to be facilitatory but peripheral in love. OT administration appears to decrease anxiety by inhibiting amygdala activity. Indeed, serotonin-dependent pathways such as the amygdala appear to interact with OT (see below). These appear to be mediated by a complex interaction between pathways that link stress response to reward mechanisms. It appears therefore that initial anxiety and stress is an inherent component of early love which reaches its fulfillment through вЂњthe chillвЂќ rendered by love and deep relationships. Positive social interactions and pair bonding (see below) appear to alleviate stress through oxytocin (OT) facilitating security and support. Norepinephrine is also associated with peripheral sympathetic nervous systems including increased heart rate, sweating trembling which may explain this experience in love. Increased activity of norepinephrine generally produces alertness energy sleeplessness and loss of appetite, increased attention, and increased memory for new stimuli which characterize (the earlier) phases of human love. Irrespective, this stress response appears to be important in the formation of social contact and attachment.Д¬entral norepinephrine may also be involved. This вЂњlove induced hypercortisolemiaвЂќ may represent a nonspecific stress response to change that characterizes early phases of relationships or a physiologic state of alertness that may help overcome neophobia. Indeed, subjects in love show higher levels of cortisol when compared to controls. Indeed, some of the signs commonly associated with love-anxiety palpitations increased peristalsis are manifestations of the stress response (albeit in a pleasurable way). Within a homeostatic range, stress-related physiologic processes including the hormones of the hypothalamo-pituitary adrenal axis can help develop and promote social bonding. As a norm, moderate stress encourages social interaction. Stress appears to be the trigger for a quest for pleasure, proximity, and closeness. The early phase of love represents an extreme neurobiological state somewhat contradictory in a physiologic sense from subsequent phases and states. S TRESS AS AN I NITIATOR/F ACILITATOR OF L OVE

Love on the brain