The anatomical basis of fear and anxiety in humans has not been definitively established; however, through the use of animal models of stress and conditioned fear, particularly those of Pavlovian fear conditioning and fear potentiated startle,10 a basic model of normal fear responding has been developed and refined. While anxiety is not identical to fear, it is closely linked to fear responding. From these preclinical studies, a 'fear neurocircuitry' has been proposed, which involves an extended anatomical network that centers on the critical involvement of the amygdala (AMYG), located in the anterior part of the medial temporal lobe.11

The AMYG is comprised of numerous subnuclei that include the basolateral complex (BLC; lateral, basal, and accessory basal nuclei) and the central nucleus (CeA; anterior, medial, and lateral nuclei). Together, these nuclei receive and process sensory input necessary for assessment of a potentially threatening stimulus, incorporate memory and prior experience into this appraisal, and coordinate the autonomic and behavioral components of fear responding. In addition to extensive 'cross-talk' and reciprocity between nuclei within the AMYG many additional structures function with the AMYG during fear learning. Key among these are the sensory thalamus and cortices, additional mesiotemporal nuclei, the orbital and medial prefrontal cortex, the anterior insula, the hypothalamus, and multiple brainstem nuclei. A schematic of this circuitry can be found in Figure 1.12

Sensory information that is vital to threat assessment is received by the AMYG via two pathways, a monosynaptic pathway from the anterior thalamus and a polysynaptic pathway from sensory cortical areas. Projections from sensory thalamus to lateral AMYG are thought to be involved in rapid conditioning to simple auditory and visual features of a stimulus, while projections from primary sensory and sensory association cortices to lateral AMYG appear to be involved in conditioned responses to more complex sensory stimuli. The most extensive extra-AMYG projections to the sensory thalamus are reciprocal to the basal and accessory basal amygdalar nuclei and these nuclei are thought to be involved in the development of long-lasting memory traces for fear conditioning.13

In addition to the reception of sensory information, the AMYG facilitates the acquisition of additional information regarding specific threats via reciprocal projections to subcortical and limbic cortical regions. The rostral perirhinal cortex, the anterior insula, and the hippocampus are particularly involved in modulation of contextual fear, providing information to the AMYG about the context of a potentially threatening stimulus or situation. In addition to a role in spatial contextual conditioning, projections from the hippocampus to the AMYG provide information about the environment that is retrieved from specific memory stores. The medial frontal cortex (mFC), including infralimbic,

How To Win Your War Against Anxiety Disorders

How To Win Your War Against Anxiety Disorders

Tips And Tricks For Relieving Anxiety... Fast Everyone feels anxious sometimes. Whether work is getting to us or we're simply having hard time managing all that we have to do, we can feel overwhelmed and worried that we might not be able to manage it all. When these feelings hit, we don't have to suffer. By taking some simple steps, you can begin to create a calmer attitude, one that not only helps you feel better, but one that allows you the chance to make better decisions about what you need to do next.

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