The Male Brain (20 page)

soared twentyfold
: Larsen 2003. For more on testosterone, androgens, and adrenarche, see Nakamura 2009 and Peper 2009a.

that emerge from his brain
: Halpern 1998 found that when teen boys go through puberty, there is a big change in sexual and aggressive thoughts. Scientists agree that testosterone is the main driver of sex differences in aggression. Aggression and testosterone are reviewed in Archer 2006 and Terburg 2009.

lengthen and thicken his penis
: Larsen 2003. During puberty the non-erect penis doubles in length. In boys, the fastest growth spurt in height occurs three years after puberty onset.

as those in girls' brains
: Swaab 1985 and 2009.
the forefront of his mind
: Halpern 1998 found that higher levels of testosterone were associated with first sexual intercourse. As puberty progresses, testosterone acts more effectively in the teen boy brain's amygdala, hypothalamus, and spinal cord, stimulating mating behavior and copulation. Reviewed in Archer 2006, King 2008, and Becker 2008a.

if they're turning into "pervs"
: Testosterone not only saves cells from being killed off in the male spinal cord and brain's visual cortex; it primes the visual cortex to focus on sexually attractive females. Some men recall when their brain's visual perception changed at puberty and, almost overnight, all it took was the
hint
of a female shape to snap their heads around. In females, two out of three of these special sex cells in the spinal cord die due to lack of testosterone. For more on cell death in the spinal cord, see Nunez 2000 and Breedlove 1983. In gay male teens the brain begins responding to visual cues from same-sex faces, body parts, and pheromones of other males. Narring 2003 found that 2.9 percent of boys by age 16-20 report same-sex attraction.

girls, which runs on autopilot
: During puberty, increases in dopamine in the sex center and copulation center increase sexual motivation and stimulate visual imagery. According to Witelson 1991, this brain area is 2.0 to 2.5 times larger in the human male than in the female. Becker 2008b found that increased dopamine in this brain area is linked to increased sexual motivation. For more on sexual motivation in the male brain, see Yeh 2009, Halpern 1998, Eme 2007, and Balthazart 2007.

always on in the background
: Becker 2008a found that in the male brain after puberty, sexual "motivation and sperm production are switched to the 'on' position all the time."

a companion hormone called vasopressin
: For more on vasopressin regulation by testosterone, see Pak 2009. Devries 2008 found that the vasopressin innervation of the brain shows perhaps the most consistent neural sex difference and that males have more vasopressin (VP) neurons and denser projections from these areas than do females, and that VP helps defeminize sex behavior in males. Researchers have found that sex differences in VP also match sex differences in social behaviors, for example, aggressive behavior. For reviews of hormones, sex, and behavior, see Becker 2008b, Gleason 2009, Forger 2009, and Pfaff 2002. For more on the opposite effects of vasopressin and oxytocin, see Viviani 2008.

to his status or turf
: Testosterone surges at puberty, so it ensures that when needed under the stress of male-male competition for sexually receptive females or procuring the resources necessary to attract such females, young men will be ready. And at the same time these surges of testosterone will
lower the sensitivity to punishment
and increase the sensitivity to reward. For overview, see Archer 2006. For more on testosterone and behavior, see Dabbs 1996, Van Honk 2004, Handa 2008, Becker 2008a, and Evuarherhe 2009.

living in status-conscious hierarchical groups
: Behrens 2009 explains how the brain develops networks for living in status-conscious groups and for hierarchical social behavior. They found that two distinct networks of brain regions are particularly active. The first area is for learning about reward and reinforcement. The second is a network that is active when a person must make estimates of another person's hostile versus friendly intentions.

from the bottom as possible
: For more on testosterone, the need for dominance, and why some people strive for high status, whereas others actively avoid it, see Josephs 2006.

that get them into trouble
: For more on risky decision making and good judgment in the brain, see Weber 2008. For more on men, risky financial behavior, and testosterone, see Dreber 2009 and Coates 2008.

began when he entered puberty
: Giedd 1996 and Lenroot
2007 found that the total cerebral volume peaks at age
10.5 in females and 14.5 in males. For more on brain development in puberty, see Berns 2009, Herve 2009, and van Duijvenvoorde 2008.

"late teens or early twenties"
: For more on teen brain development, see Cameron 2005, Luna 2004b, Tiemeier 2010, Giedd 1996 and 2006, and Schweinsburg 2005.
to focus on his studies
: For more on adolescent mental development, see Yurgelun-Todd 2007 and Ochsner 2004.

his sex and aggression circuits
: Trainor 2004 found that a surge in testosterone following an aggressive encounter caused males to behave more aggressively in another encounter the following day. For more on testosterone and vasopressin, see Young 2009a, Neumann 2008b, Raggenbass 2008, Kajantie 2006, Schulz 2006a, Thompson 2006, and Keverne 2004. For reviews of neuroscience, sex, psychology, and testosterone, see Becker 2008a, Eme 2007, and Archer 2006.

center--the amygdala--would activate
: The major role of the amygdala is in alerting the brain to danger, thus triggering fear and anxiety. Debiec 2005 found that in the amygdala, vasopressin (whose manufacture is stimulated by testosterone) and oxytocin (whose manufacture is stimulated by estrogen) work in opposite directions. For more on sex hormones and behavior, see Huber 2005, Pittman 2005, Donaldson 2008, Herry 2008, Tsunematsu 2008, Viviani 2008, and Bolshakov 2009.

homework just doesn't do it
: Williamson 2008 found that cortisol, the stress hormone, starts to have less and less activating effect on the male brain as testosterone and dopamine rise. Thus it takes more and more excitement to get the brain's attention. For more on the down-regulation effects at puberty on the male brain by dopamine, see Becker 2008a.

high-school dropouts are boys
: National Center for Education Statistics. For more, see Dropout rates in the United States, 2004. National Council on Education 2009.

brains require at least ten
: Hagenauer 2009 found that this sleep deprivation is due to pubertal changes in the homeostatic and circadian regulation of sleep, promoting a delayed sleep phase for later bedtimes. For more on sleep disorders in teens, see Crowley 2007.

to be excited about anything
: Becker 2008a: The baseline, or set-point, in boys changes, becoming less reactive. For more on emotional and cognitive changes during adolescence, see Yurgelun-Todd 2007.

area in adults and children
: McClure 2004. And for more on pleasure, reward, and risk in the brain, see Bornovalova 2009.

feel normal levels of stimulation
: Becker 2008a found that the masculinizing and feminizing of the dopamine motivation system increases in the brain at puberty.

much as children's or adults'
: McClure 2004. For reviews, see Becker 2008b, Steinberg 2004a, Teicher 2000, Keating 2004, and Paus 2009.

how different her outlook would be
: Response to threat and protection of territory change at puberty. Archer 2006 found that preliminary evidence from fMRI studies suggests
amygdala
a relationship between testosterone and responsiveness to anger in faces, perhaps

by modifying
hormone levels behaviors. Even in childhood, hormones were acting to prime behavior, just at lower levels. For more on testosterone priming boys' behavior, see Archer 2006, Finkelstein 1997, De Vries 1998, Van Honk 2004, and Dabbs 1996.

teen boy's sense of reality
: Thompson 2004. For more on vasopressin neurons whose projections extend deep into the male brain, see Caldwell 2008.

way teen girls perceive reality
: See Carter 2009 for overview of oxytocin and vasopressin and social behavior in males and females. For more on the underlying neuroscience behind gender differences, see Becker 2008b.

for aggressive and territorial behaviors
: Craig I. 2009, O'Connor 2004, and Archer 2009 and 2006. See Becker 2008a for perception and motivation changes in the male and female brains.

squirt of vasopressin nasal spray
: Thompson 2006 showed that giving males extra vasopressin stimulates angry and competitive facial expressions in response to seeing the faces of unfamiliar males. For more on changes in male brain responses to faces from teen years to middle age, see Deeley 2008.

more territorial aggression and mate protection
: Gobrogge 2007 found that males who were pair-bonded to a female for two weeks displayed intense levels of aggression toward strangers. They hypothesize that dopamine and vasopressin in the hypothalamus may be involved in the regulation of enduring aggression associated with pair bonding in males.

of facial posturing and bluffing
: See Sonnby-Borgstrom 2008 for more on facial posturing and gender differences in facial imitation, emotional contagion, and regulation of facial expression.
is used to maintain power
: Archer 2006 found that in societies where the dominant male's display of anger enforces order, angry faces serve an important purpose. The battles for dominance in the primate kingdom, where the alpha male stares down his opponent and the loser male averts his eyes, are observed in humans, too--so much so that high testosterone is associated with staring endurance, or face-to-face dominance. Men with less testosterone have been shown to exhibit more submissive behavior by breaking eye contact, looking down and away.

highest testosterone, according to research
: Archer 2006. Rowe 2004, who analyzed testosterone in boys aged 9-15, found that the dramatically increasing testosterone in pubescent boys contributed to social dominance and leadership status.

being more irritable and impatient
: Olweus 1988 found that high levels of testosterone made boys more impatient and irritable, which in turn increased their propensity to engage in aggressive-destructive behavior.

the brain circuits for aggression
: Wirth 2007. For more on angry faces and testosterone, see Van Honk 2005 and Delville 1996.

than he did before adolescence
: Rymarczyk 2007.
between girls' and boys' brains
: Rymarczyk 2007 found a sex difference in the brain's processing of tone of voice. For more on sex differences in brain chemistry and the sex-determining gene located on the Y chromosome, see Wu 2009 and Paus 2009.

they processed the sound of music
: Ruytjens 2007 found the male brain screened out white noise better than the female brain. For more on gender differences in auditory processing, see Voyer 2001 and Ikezawa 2008.

than the female brain does
: Ruytjens 2007. For more on fetal brain development and the effects of testosterone on hearing, see Beech 2006 and Cohen-Bendahan 2004.

musical banter was practically
2002 studied sex differences in emotional words, and found the tone and meaning of emotional words were processed faster in females than in males.

the hot substitute teacher's measurements
: Guiller 2007 found gender differences in students' linguistic behavior online and in text messages. Fox 2007 studied gender differences in instant messaging and found that women sent messages that were more emotionally expressive than those sent by men. For more on sex differences in language, see Ullman 2008.

girls about people and relationships
: For more on how women and men use language differently and talk about different topics, see Tannen 1990. Women use words that reflect social concerns; men refer to more concrete objects and impersonal topics. Newman 2008 examined over 14,000 text files and found that women used more words related to psychological and social processes. Men referred more to object properties and impersonal topics. For more research on gender differences in language use, see Tannen 1997, Leaper 2007, and Ullman 2008.