Dispersion And Functions Of Fear Systems In The Brain Continuing Studies Of The Neuroanatomy Of Fear

Modern neuroscience techniques can now estimate the widespread influences of fear within the brain. Immunocytochemical visualization of the genetic transcription and translation of growth-promoting oncogenes, such as c-fos, have allowed investigators to monitor the cerebral consequences of many fear-provoking stimuli, including foot shock (Beck and Fibiger, 1995), nonpainful threatening stimuli, such as environments that have been paired with aversive events (Silveira et al., 1993), as well as the effects of direct activation of FEAR circuits following brain stimulation (Silveira et al., 1995). Not only is there abundant arousal of brain areas from the PAG to the amygdala, there is typically massive cortical activation, especially if animals are tested while awake as opposed to anesthetized. Similar patterns of neuronal activation are evident in animals defeated during fighting (Kollack-Walker et al., 1997), during exposure to predators (Dielenberg et al., 2001), and even in animals simply exposed to the fearful 22-kHz distress squeals of conspecifics (Beckett et al., 1997). Such work is revealing neural details, both anatomical and neurochemical, that no human brain imaging yet approximates.

These widespread changes evident in animal brains can be contrasted with the relatively modest brain effects documented in humans in functional magnetic resonance imaging (fMRI) and positron emission tomography (PET). Such studies [for a full review, see Phan et al. (2002) and Zald (2003)], even when conducted on chronically anxious individuals, typically yield highly restricted regional arousals in areas such as the amygdala (Irwin et al., 1996; Rauch et al., 1995). In part, this is explained simply by the fact that the utilization of group statistics often masks the more widespread brain effects seen in individual subjects. The modest effects are also, in part, due to the use of comparatively weak cognitive-type fear stimuli (e.g., angry faces, etc.). Also, certain technologies (e.g., fMRI approaches) may not yet have the resolution to highlight many of the subcortical brain areas that are, in fact, aroused during fear using more sensitive tools (Damasio et al., 2000, and also see Chapter 2).

Anxiety and Depression 101

Anxiety and Depression 101

Everything you ever wanted to know about. We have been discussing depression and anxiety and how different information that is out on the market only seems to target one particular cure for these two common conditions that seem to walk hand in hand.

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