The early phase of love represents an extreme neurobiological state somewhat contradictory in a physiologic sense from subsequent phases and states. Stress appears to be the trigger for a quest for pleasure, proximity, and closeness. As a norm, moderate stress encourages social interaction.

Within a homeostatic range, stress-related physiologic processes including the hormones of the hypothalamo-pituitary adrenal axis can help develop and promote social bonding. Indeed, some of the signs commonly associated with love-anxiety palpitations increased peristalsis are manifestations of the stress response (albeit in a pleasurable way). Indeed, subjects in love show higher levels of cortisol when compared to controls. Irrespective, this stress response appears to be important in the formation of social contact and attachment.

This “love induced hypercortisolemia” 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

Central norepinephrine may also be involved. 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. Norepinephrine is also associated with peripheral sympathetic nervous systems including increased heart rate, sweating trembling which may explain this experience in love.

Positive social interactions and pair bonding (see below) appear to alleviate stress through oxytocin (OT) facilitating security and support. It appears therefore that initial anxiety and stress is an inherent component of early love which reaches its fulfillment through “the chill” rendered by love and deep relationships. These appear to be mediated by a complex interaction between pathways that link stress response to reward mechanisms. Indeed, serotonin-dependent pathways such Romanian naiset, jotka haluavat pГ¤ivГ¤määriГ¤ as the amygdala appear to interact with OT (see below). OT administration appears to ygdala activity.

G ONADAL H ORMONES

The role of gonadal hormones in this regard appears to be facilitatory but peripheral in love. Sex hormones ental effects on neural systems involved in social attachments and may mediate both genetic and environmental influences on the propensity to love and form attachments. Testosterone receptors are distributed in the hypothalamus. Testosterone through these receptors may suppress levels or activity of serotonin which apparently increases aggressiveness. Testosterone further enhances vasopressin levels in the medial amygdala lateral hypothalamus and pre-optical medial area which are involved in aggressive behaviors. Gonadal hormones may further regulate OT and vasopressin through indirect mechanisms. 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.

Gender differences evident on functional imaging in the partner preference and early phases of love warrant mention. Men show more activity in a region of the right posterior dorsal insula (an area correlating with penile turgidity and viewing of beautiful faces) and in regions associated with the integration of visual stimuli. Women tend to show more activity than men in regions associated with attention, memory, and emotion. Courting men respond more strongly than women to visual signals of youth and beauty. Women appear to be more attracted to men who offer status and resources.

Pair bonding is a very bland scientific term for enduring (romantic) relationships (attachment) and is seen in OVE AS A R EWARD

From the very beginning of our efforts, in understanding the biologic basis of love it has been clear that it involves reward centers in the brains. In this love and addictions (such as by drugs) are somewhat interconnected the one key difference is that naturally rewarding activities such as love are controlled by feedback mechanisms that activate aversive centers that limit the destructive qualities of addiction seen with drugs. Love activates specific regions in the reward system. The effects include a reduction in emotional judgment and reduced fear and also reduced depression and enhanced mood. It also leads to a reduced need to assess the social validity of that person. It thus appears to deactivate areas mediating negative emotions, avoidance behavior critical social assessment and, on the other hand, triggers mechanisms involved in pleasure reward and appetitive motivation [ Figure 1 ].