patients with normal cognitive function will
have a mild tendency to grasp the first time the
reflex is attempted, but a request not to grasp
the examiner quickly abolishes the response.
Patients who are unable to inhibit the reflex
invariably have prefrontal pathology. The grasp
reflex may be asymmetric if the prefrontal in-
jury is greater on one side, but probably re-
quires some impairment of both hemispheres,
as small, unilateral lesions rarely cause grasp-
ing.
137
Grasping disappears when the lesion
involves the motor cortex and causes hemi-
paresis. It is of greatest value in a sleepy pa-
tient who can cooperate with the exam; it dis-
appears as the patient becomes more drowsy.
Like paratonia, prefrontal reflexes are normally
present in young infants, but disappear as the
forebrain matures.
135
Motor Responses
After assessing muscle tone, the examiner next
tests the patient for best motor response to
sensory stimulation (Figure 2–10). If the pa-
tient does not respond to voice or gentle shak-
ing, arousability and motor responses are tes-
ted by painful stimuli. The maneuvers used
to provide adequate stimuli without inducing
actual tissue damage are shown in Figure 2–1.
A Metabolic encephalopathy
B Upper midbrain damage
C Upper pontine damage
Figure 2–10. Motor responses to noxious stimulation in patients with acute cerebral dysfunction. Levels of associated
brain dysfunction are roughly indicated at left. Patients with forebrain or diencephalic lesions often have a hemiparesis
(note lack of motor response with left arm, externally rotated left foot, and left extensor plantar response), but can gen-
erally make purposeful movements with the opposite side. Lesions involving the junction of the diencephalon and the mid-
brain may show decorticate posturing, including flexion of the upper extremities and extension of the lower extremities. As
the lesion progresses into the midbrain, there is generally a shift to decerebrate posturing (C), in which there is extensor
posturing of both upper and lower extremities. (From Saper, C. Brain stem modulation of sensation, movement, and con-
sciousness. Chapter 45 in: Kandel, ER, Schwartz, JH, Jessel, TM. Principles of Neural Science. 4th ed. McGraw-Hill, New
York, 2000, pp. 871–909. By permission of McGraw-Hill.)
Examination of the Comatose Patient
73
Responses are graded as appropriate, inap-
propriate, or no response. An appropriate re-
sponse is one that attempts to escape the stim-
ulus, such as pushing the stimulus away or
attempting to avoid the stimulus. The motor
response may be accompanied by a facial gri-
mace or generalized increase in movement. It
is necessary to distinguish an attempt to avoid
the stimulus, which indicates intact sensory
and motor connections within the spinal cord
and brainstem, from a stereotyped withdrawal
response, such as a triple flexion withdrawal of
the lower extremity or flexion at the fingers,
wrist, and elbow. The stereotyped withdrawal
response is not responsive to the nature of the
stimulus (e.g., if the pain is supplied over the
dorsum of the toe, the foot will withdraw into,
rather than away from, the stimulus) and thus
is not appropriate to the stimulus that is ap-
plied. These spinal level motor patterns may
occur in patients with severe brain injuries or
even brain death. It is also important to assess
asymmetries of response. Failure to withdraw
on one side may indicate either a sensory or a
motor impairment, but if there is evidence of
facial grimacing, an increase in blood pressure
or pupillary dilation, or movement of the con-
tralateral side, the defect is motor. Failure to
withdraw on both sides, accompanied by facial
grimacing, may indicate bilateral motor im-
pairment below the level of the pons.
Posturing responses include several stereo-
typed postures of the trunk and extremities.
Most appear only in response to noxious stim-
uli or are greatly exaggerated by such stimuli.
Seemingly spontaneous posturing most often
represents the response to endogenous stim-
uli, ranging from meningeal irritation to an oc-
cult bodily injury to an overdistended bladder.
The nature of the posturing ranges from flexor
spasms to extensor spasms to rigidity, and may
vary according to the site and severity of the
brain injury and the site at which the nox-
ious stimulation is applied. In addition, the two
sides of the body may show different patterns
of response, reflecting the distribution of in-
jury to the brain.
Clinical tradition has transferred the terms
decorticate rigidity and decerebrate rigidity
from experimental physiology to certain pat-
terns of motor abnormality seen in humans.
This custom is unfortunate for two reasons.
First, these terms imply more than we really
know about the site of the underlying neuro-
logic impairment. Even in experimental ani-
mals, these patterns of motor response may be
produced by brain lesions of several different
kinds and locations and the patterns of motor
response in an individual to any one of these
lesions may vary across time. In humans, both
types of responses can be produced by supra-
tentorial lesions, although they imply at least
incipient brainstem injury. There is a tendency
for lesions that cause decorticate rigidity to be
more rostral and less severe than those caus-
ing decerebrate rigidity. In general, there is
much greater agreement among observers if
they simply describe the movements that are
seen rather than attempt to fit them to com-
plex patterns.
Flexor posturing of the upper extremities
and extension of the lower extremities corre-
sponds to the pattern of movement also called
decorticate posturing. The fully developed
response consists of a relatively slow (as op-
posed to quick withdrawal) flexion of the arm,
wrist, and fingers with adduction in the upper
extremity and extension, internal rotation, and
vigorous plantar flexion of the lower extremity.
However, decorticate posturing is often frag-
mentary or asymmetric, and it may consist of
as little as flexion posturing of one arm. Such
fragmentary patterns have the same localizing
significance as the fully developed postural
change, but often reflect either a less irritating
or smaller central lesion.
The decorticate pattern is generally pro-
duced by extensive lesions involving dysfunc-
tion of the forebrain down to the level of the
rostral midbrain. Such patients typically have
normal ocular motility. A similar pattern of
motor response may be seen in patients with
a variety of metabolic disorders or intoxica-
tions.
138
However, the presence of decorticate
posturing in cases of brain injury is ominous.
For example, in the series of Jennett and
Teasdale, after head trauma only 37% of co-
matose patients with decorticate posturing
recovered.
139
Even more ominous is the presence of ex-
tensor posturing of both the upper and lower
extremities, often called decerebrate postur-
ing. The arms are held in adduction and ex-
tension with the wrists fully pronated. Some
patients assume an opisthotonic posture, with
teeth clenched and arching of the spine. Tonic
neck reflexes (rotation of the head causes hy-
perextension of the arm on the side toward
74
Plum and Posner’s Diagnosis of Stupor and Coma