Primitive reflexes & frontal release signs

" Frontal release signs are primitive reflexes traditionally held to be a sign of disorders that affect the frontal lobes (clinical examination video clips found below)."

The only reflex thought to have good localizing value is the palmar grasp reflex which usually signifies damage to the frontal lobe of the opposite side. The glabellar reflex or "glabellar tap" is also present in individuals with extrapyramidal disorders such as parkinson's disease. Conceptually, these reflexes are "hard-wired" before birth and are therefore able to be elicited in the newborn. As the brain matures, certain areas (usually within the frontal lobes) exert an inhibitory effect thus causing the reflex to disappear. When disease processes disrupt these inhibitory pathways the response is "released" from its inhibitory shackles and elicitable once again, hence the term "frontal release sign".

Whilst the evolutionary value of some of these responses is clear, the role in infancy of the palmomental reflex remains a mystery and therefore may be a phylogenetic remnant.

Some frontal release signs and their role in infancy:

* Palmar grasp:- Baby naturally grabs objects.
* Palmomental response:- unknown.
* Rooting:- Baby finds breast to suckle.
* Sucking:- Baby sucks breast / bottle teat to get milk.
* Snout reflex:- Involved in suckling.
* Glabellar reflex:- May protect eyes in certain situations.

Eliciting the palmomental response by stimulation of the skin over the thenar eminence

A one-sided palmomental response is seen on the left side only

References

1) Marinesco G, Radovici A (1920). "Sur un reflexe cutane nouveau: reflexe palmo-mentonnier". Rev Neurol 27: 237-40.

2) Owen G, Mulley GP (2002). "The palmomental reflex: a useful clinical sign?". J. Neurol. Neurosurg. Psychiatr. 73 (2): 113–5.

3) Gotkine M, Haggiag S, Abramsky O, Biran I (2005). "Lack of hemispheric localizing value of the palmomental reflex". Neurology 64 (9): 1656.