Recent Studies of Alerting Implicate Noradrenaline

Most of the foregoing discussion focused on the roles of NMTs in arousal and vigilance. However, the LC/ NA system is also involved in alerting in that it reacts phasically to unexpected environmental stimuli. If the LC is damaged, alerting responses to intense, novel stimuli are impaired.

A particularly attractive paradigm for studying alerting is the cued target detection task developed by Michael Posner. This task, which was developed to study covert movements of attention, investigates the effects of visual cues on reaction times to peripheral targets. Two cues, valid and invalid, are included to assess the impact of spatial information on the speed of covert orienting. Two additional cues, neutral and no-cue, are included as controls to specifically assess alerting effects. The difference in reaction times between valid and invalid trials is termed the validity effect, and the difference between neutral and no-cue trials is known as the alerting effect. The question is how altered levels of NA or DA affect the validity and alerting effects. The results confirm that lowered levels of NA produced by a2 receptor blockers significantly reduce the size of the alerting effect. a2 agonists have the opposite effects. None of these substances alter the validity effect. These results are also consistent with those of studies using cellular monitoring of LC activity, which suggest that LC activity is associated with attentional lability. That is, when the subject attends to the fixation point, presentation of the peripheral stimulus evokes a major LC response because it is unexpected and located away from the current focus of attention. The presence of the adrenergic agonist, however, reduces LC activity and produces a state of attentional fixity within which reaction times are slowed.

Breaking Bulimia

Breaking Bulimia

We have all been there: turning to the refrigerator if feeling lonely or bored or indulging in seconds or thirds if strained. But if you suffer from bulimia, the from time to time urge to overeat is more like an obsession.

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