Phylogenetic threats such as spiders evoke our deepest primitive fears. When close or looming, such threats engage evolutionarily conserved monitoring systems and defense reactions that promote self-preservation. With the use of a modified behavioral approach task within functional MRI, we show that, as a tarantula was placed closer to a subject's foot, increased experiences of fear coincided with augmented activity in a cascade of fear-related brain networks including the periaqueductal gray, amygdala, and bed nucleus of the stria terminalis. Activity in the amygdala was also associated with underprediction of the tarantula's threat value and, in addition to the bed nucleus of the stria terminalis, with monitoring the tarantula's threat value as indexed by its direction of movement. Conversely, the orbitofrontal cortex was engaged as the tarantula grew more distant, suggesting that this region emits safety signals or expels fear. Our findings fractionate the neurobiological mechanisms associated with basic fear and potentially illuminate the perturbed reactions that characterize clinical phobias.expectancy errors | imminence | distance E volutionary pressures have selected for mechanisms that encourage the avoidance of close or looming threat (1-3). In humans, this innate capacity is particularly evident with phylogenetic threats such as spiders, which rate among the most ubiquitous of phobias (4). For example, in everyday life it is common to experience a primal surge of terror when a spider crawls within our personal space, yet we may observe a distant spider without trepidation. In the clinical setting, behavioral approach tasks are used to expose phobic patients to phobogenic stimuli (e.g., spiders or snakes) at varying distances to evaluate and treat their fear responses. Such approaching threats elicit precipitous increases in subjective fear and autonomic arousal (5, 6), which are characteristics of the exaggerated emotional responses observed in phobic subjects.Research in rodents has shown that encountering a distant or close natural predator (e.g., a cat) evokes distinct defense reactions in the form of behavioral quiescence and vigorous flight, respectively (7). In humans, functional neuroimaging has begun to reveal the brain networks implicated in such situations of immediate danger. One study showed that the active avoidance of an artificial predator with the ability to chase, capture, and inflict pain resulted in brain activity switching from ventromedial prefrontal cortex to the midbrain, including the periaqueductal gray (PAG), as the threat became more imminent (8). Two recent studies have also shown that tracking the increasing proximity of a shock stimulus is associated with activity in the bed nucleus of the stria terminalis (BNST), a region highly connected to the amygdala (9), whereas courage associated with self-administered movement of a snake toward the subject's own head increases activating the ventromedial prefrontal cortex (10). These studies point to an anatomical network involved ...

Humans appear to have an inherent prosocial tendency toward one another in that we often take pleasure in seeing others succeed. This fact is almost certainly exploited by game shows, yet why watching others win elicits a pleasurable vicarious rewarding feeling in the absence of personal economic gain is unclear. One explanation is that game shows use contestants who have similarities to the viewing population, thereby kindling kin-motivated responses (for example, prosocial behavior). Using a game show-inspired paradigm, we show that the interactions between the ventral striatum and anterior cingulate cortex subserve the modulation of vicarious reward by similarity, respectively. Our results support studies showing that similarity acts as a proximate neurobiological mechanism where prosocial behavior extends to unrelated strangers.

Chronic low back pain is a common neurological disorder. The periaqueductal gray (PAG) plays a key role in the descending modulation of pain. In this study, we investigated brain resting state PAG functional connectivity (FC) differences between patients with chronic low back pain (cLBP) in low pain or high pain condition and matched healthy controls (HCs). PAG seed based functional connectivity (FC) analysis of the functional MR imaging data was performed to investigate the difference among the connectivity maps in the cLBP in the low or high pain condition and HC groups as well as within the cLBP at differing endogenous back pain intensities. Results showed that FC between the PAG and the ventral medial prefrontal cortex (vmPFC)/rostral anterior cingulate cortex (rACC) increased in cLBP patients compared to matched controls. In addition, we also found significant negative correlations between pain ratings and PAG–vmPFC/rACC FC in cLBP patients after pain-inducing maneuver. The duration of cLBP was negatively correlated with PAG–insula and PAG–amygdala FC before pain-inducing maneuver in the patient group. These findings are in line with the impairments of the descending pain modulation reported in patients with cLBP. Our results provide evidence showing that cLBP patients have abnormal FC in PAG centered pain modulation network during rest.