The clenching-grinding spectrum and fear circuitry disorders: clinical insights from the neuroscience/paleoanthropology interface

This review discusses the clenching-grinding spectrum from the neuropsychiatric/neuroevolutionary perspective. In neuropsychiatry, signs of jaw clenching may be a useful objective marker for detecting or substantiating a self-report of current subjective emotional distress. Similarly, accelerated tooth wear may be an objective clinical sign for detecting, or substantiating, long-lasting anxiety. Clenching-grinding behaviors affect at least 8 percent of the population. We argue that during the early paleolithic environment of evolutionary adaptedness, jaw clenching was an adaptive trait because it rapidly strengthened the masseter and temporalis muscles, enabling a stronger, deeper and therefore more lethal bite in expectation of conflict (warfare) with conspecifics. Similarly, sharper incisors produced by teeth grinding may have served as weaponry during early human combat. We posit that alleles predisposing to fear-induced clenching-grinding were evolutionarily conserved in the human clade (lineage) since they remained adaptive for anatomically and mitochondrially modern humans (Homo sapiens) well into the mid-paleolithic. Clenching-grinding, sleep bruxism, myofacial pain, craniomaxillofacial musculoskeletal pain, temporomandibular disorders, oro-facial pain, and the fibromyalgia/chronic fatigue spectrum disorders are linked. A 2003 Cochrane meta-analysis concluded that dental procedures for the above spectrum disorders are not evidence based. There is a need for early detection of clenching-grinding in anxiety disorder clinics and for research into science-based interventions. Finally, research needs to examine the possible utility of incorporating physical signs into Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition posttraumatic stress disorder diagnostic criteria. One of the diagnostic criterion that may need to undergo a revision in Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition is Criterion D (persistent fear-circuitry activation not present before the trauma). Grinding-induced incisor wear, and clenching-induced palpable masseter tenderness may be examples of such objective physical signs of persistent fear-circuitry activation (posttraumatic stress disorder Criterion D).     

Book Reviews

J oseph C ampbell : Creative mythology
E leanor B ertine : Jung's contribution to our time
M ichael B alint : The basic fault
H einrich R acker : Transference and counter-transference
D avid B akan : Disease, pain and sacrifice
A senath P etrie : Individuality in pain and suffering
B runo B ettelheim : The empty fortress: infantile autism and the birth of the self
P aul R oazen : Freud: political and social thought
J oel A llison , S. J. B latt and C. N. Z imet : The interpretation of psychological tests
C harles R ycroft : Anxiety and neurosis
A nthony S torr : Human aggression
M ichael C ourtenay : Sexual discord in marriage
J olande J acobi . Frauenprobleme, Eheprobleme
J. M. H eaton : The Eye; phenomenology and psychology of function and disorder     

The Adaptive Significance of Sexual Conditioning: Pavlovian Control of Sperm Release

Male quail received Pavlovian conditioning trials that consisted of placement in a distinctive experimental chamber (the conditioned stimulus) paired with the opportunity to copulate with a female (the unconditioned stimulus). For control subjects, exposures to the conditioned and unconditioned stimuli were unpaired. After four and six trials, each subject was placed in the experimental chamber with a probe stimulus that included some of the visual cues of a female's head and neck. Pavlovian conditioning increased how much time subjects spent near the probe stimulus. Conditioned subjects also released greater volumes of semen and greater numbers of spermatozoa than the control subjects. Significant differences were not obtained in serum testosterone levels or in other measures of sperm quality. These results demonstrate that sexual Pavlovian conditioning can affect reflexes involved in sperm release and thereby modulate reproductive fitness.     

Effects of Predator-Induced Stress and Age on Working Memory in Rats

The Psychological Record - The effects of age and predator-induced stress, by exposing rats to a cat, were examined during subsequent testing of spatial working memory. Male rats (3 months and 20...     

Wittgensteinian Accounts of Moorean Absurdity

Philosophical Studies -