Decades of research has established the essential involvement of the brain limbic system in emotional behavior. The amygdala is a very well attended component of the limbic system. Divergent outputs to other limbic and extra-limbic systems make the amygdala a key component in the initiation of coherent emotional responses (Davis, 1992 and Davis & Whalen, 2001). Afferents from the thalamus enable the amygdala to evaluate the emotional valence of aversive cues, while considering only the crude features of these cues and thus bypassing the processing of high cognitive structures (LeDoux, 1993). Involvement of the amygdala in anxiety disorders has long been suspected. Both under and overexpression of fear and anxiety were, respectively reported after induction of lesion or the stimulation of the amygdala (Aggleton, 1993, Chapman et al., 1954 and Gloor, 1992). Combined with recent neuroimaging findings (Birbaumer et al., 1998 and Rauch et al., 2000), there is sufficient evidence that limbic/amygdaloid pathology is causally involved in anxiety disorders.
An alternative view holds that limbic malfunction is not a necessary prerequisite for anxiety disorders. Rather, anxiety may reflect an excessive response of the normal limbic system interacting with abnormally functioning extra-limbic structures. This view is consistent with frequently reported comorbidity of anxiety with neurological disorders, such as dizziness, vertigo, imbalance, and vestibular dysfunction (Sklare, Konrad, Maser, & Jacob, 2001). To mention a few examples from recent extensive review, fear and emotional displeasure are frequently associated with incidents of acute vertigo and motion sickness (see review by Balaban & Thayer, 2001). Patients with even mild vertiginous symptoms score high on the State-Trait Anxiety Scale (Alvord, 1991). Dizziness and vestibular dysfunction prevail in panic disorder patients during and between panic attacks (Jacob, Furman, & Balaban, 1996a; Jacob, Furman, Durrant, & Turner, 1996c; Sklare, Stein, Pikus, & Uhde, 1990). Balance dysfunction is related to agoraphobic avoidance in panic disorder patients (Jacob et al., 1996c), while vestibular dysfunction is related to height phobia (in Jacob, Redfern, & Furman, 1995). These observations are not only confined to clinical samples, as correlation between dizziness and anxiety was also confirmed in community surveys (see Yardley et al., 2001). A possible interpretation of these frequent associations is that anxiety is a byproduct of an interaction between a normal limbic system and malfunctioning balance systems.
Interaction with a malfunctioning balance system may bear particularly harsh consequences during childhood. Balance-challenging situations trigger fear responses, which are constructive in future avoidance of similarly dangerous situations (Balaban & Jacob, 2001; Yardley, Todd, Lacoudraye-Harter, & Ingham, 1992). Avoidance of balance threats may be an effective strategy for adults, as it often requires only a minor modification of their life style. An avoidance strategy seems to be less effective in children, whose environment features frequent and varied balance threats, ranging from mildly challenging situations, such as balancing on an uneven surface, to highly challenging situations, such as balancing on unstable surface. Given their frequent encounter with balance threats, children with balance disorder will experience repeated fear responses that may eventually precipitate a development of a chronic anxiety disorder. It is possible, therefore, that balance dysfunction is an important trigger for childhood anxiety.
This hypothesis is in line with findings of a high correlation between abnormal balance/vestibular symptoms and indices of anxiety in large samples of children (Levinson, 1989a, Levinson, 1989b and Levinson, 1989c). These samples included children who were referred to the clinic for learning disability and therefore it would be highly relevant to demonstrate comorbidity of anxiety and balance disorder in children referred to the clinic for anxiety disorder. Therefore, the present study tests the hypothesis that childhood anxiety disorders may be associated with balance deficiency.
