Palmomental reflex
Encyclopedia
The palmomental reflex is a primitive reflex
consisting of a twitch of the chin muscle elicited by stroking a specific part of the palm. It is present in infancy and disappears as the brain matures during childhood but may reappear due to processes that disrupt the normal cortical
inhibitory pathways. Therefore it is an example of a frontal release sign
.
(receptive) and efferent
(motor) arms of the reflex
are on the same side (ipsilateral) to the hand stimulated; however this hypothesis remains unsubstantiated.
The PMR has been found to be present more frequently in various neurological conditions both localized and diffuse. These include congenital conditions such as Down's syndrome where it is unclear whether the reflex persists throughout life or disappears and then re-appears in association with the onset of Alzheimer's disease
pathology. The reflex is common in the elderly population and should not be taken as indicative of a dementing process.
is stroked briskly with a thin stick, from proximal (edge of wrist) to distal (base of thumb) using moderate pressure. A positive response is considered if there is a single visible twitch of the ipsilateral mentalis muscle (chin muscle on the same side as the hand tested).
Primitive reflexes
such as the PMR were classically viewed as signs of disorders that affect the frontal lobe
s, however this traditional view is questionable as the reflex has been noted for example in cases of one-sided temporal lobe pathology.
A presentation at the 19th Meeting of the European Neurological Society suggests a possible link between presence of the PMR with stroke. Patients with the PMR present had a significantly higher incidence of silent ischemic strokes than matched patients who did not have the reflex present.
Primitive reflexes
Primitive reflexes are reflex actions originating in the central nervous system that are exhibited by normal infants but not neurologically intact adults, in response to particular stimuli. These reflexes disappear or are inhibited by the frontal lobes as a child moves through normal child...
consisting of a twitch of the chin muscle elicited by stroking a specific part of the palm. It is present in infancy and disappears as the brain matures during childhood but may reappear due to processes that disrupt the normal cortical
Cerebral cortex
The cerebral cortex is a sheet of neural tissue that is outermost to the cerebrum of the mammalian brain. It plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness. It is constituted of up to six horizontal layers, each of which has a different...
inhibitory pathways. Therefore it is an example of a frontal release sign
Frontal release sign
Frontal release signs are primitive reflexes traditionally held to be a sign of disorders that affect the frontal lobes. The appearance of such signs reflects the area of brain dysfunction rather than a specific disorder which may be diffuse such as a dementia, or localised such as a tumor.The only...
.
Research
Marinesco and Radovici in their seminal paper hypothesize that both the afferentAfferent
Afferent is an anatomical term with the following meanings:*Conveying towards a center, for example the afferent arterioles conveying blood towards the Bowman's capsule in the Kidney. Opposite to Efferent.*Something that so conducts, see Afferent nerve fiber...
(receptive) and efferent
Efferent
Efferent is an anatomical term with the following meanings:*Conveying away from a center, for example the efferent arterioles conveying blood away from the Bowman's capsule in the kidney. Opposite to afferent....
(motor) arms of the reflex
Reflex
A reflex action, also known as a reflex, is an involuntary and nearly instantaneous movement in response to a stimulus. A true reflex is a behavior which is mediated via the reflex arc; this does not apply to casual uses of the term 'reflex'.-See also:...
are on the same side (ipsilateral) to the hand stimulated; however this hypothesis remains unsubstantiated.
The PMR has been found to be present more frequently in various neurological conditions both localized and diffuse. These include congenital conditions such as Down's syndrome where it is unclear whether the reflex persists throughout life or disappears and then re-appears in association with the onset of Alzheimer's disease
Alzheimer's disease
Alzheimer's disease also known in medical literature as Alzheimer disease is the most common form of dementia. There is no cure for the disease, which worsens as it progresses, and eventually leads to death...
pathology. The reflex is common in the elderly population and should not be taken as indicative of a dementing process.
Eliciting and observing response
The thenar eminenceThenar eminence
The thenar eminence refers to the group of muscles on the palm of the human hand at the base of the thumb...
is stroked briskly with a thin stick, from proximal (edge of wrist) to distal (base of thumb) using moderate pressure. A positive response is considered if there is a single visible twitch of the ipsilateral mentalis muscle (chin muscle on the same side as the hand tested).
Localizing value
A study set in a neurosurgical in-patient population showed there is no significant association between the side of the reflex and the side of the hemispheric lesion in patients with unilateral (one-sided) reflexes and unilateral (one-sided) lesions.Primitive reflexes
Primitive reflexes
Primitive reflexes are reflex actions originating in the central nervous system that are exhibited by normal infants but not neurologically intact adults, in response to particular stimuli. These reflexes disappear or are inhibited by the frontal lobes as a child moves through normal child...
such as the PMR were classically viewed as signs of disorders that affect the frontal lobe
Frontal lobe
The frontal lobe is an area in the brain of humans and other mammals, located at the front of each cerebral hemisphere and positioned anterior to the parietal lobe and superior and anterior to the temporal lobes...
s, however this traditional view is questionable as the reflex has been noted for example in cases of one-sided temporal lobe pathology.
A presentation at the 19th Meeting of the European Neurological Society suggests a possible link between presence of the PMR with stroke. Patients with the PMR present had a significantly higher incidence of silent ischemic strokes than matched patients who did not have the reflex present.