Richard L. Segal

Modification of human spinal stretch reflexes: Preliminary studies

Modulation of the human spinal stretch reflex (SSR) may be important in treating hyperactive reflexes or may be a tool to enhance normal performance. Eight of 9 subjects given feedback of biceps brachii SSR amplitude and instructed to increase (uptrain) or decrease (downtrain) this response were able to do so in the appropriate direction. These results imply that, as in non-human primates, SSR amplitude can be modified.

Anatomical Partitioning of Three Multiarticular Human Muscles

To examine neuromuscular partitioning within human muscles, the innervation patterns and muscle fiber architecture of the flexor carpi radialis (FCR), extensor carpi radialis longus (ECRL) and lateral gastrocnemius (LG) muscles were examined. Consistent patterns of innervation between specimens were found within each of the three muscles. The nerve to the FCR clearly innervates three major architectural divisions of the muscle. The ECRL is innervated by two different muscle nerves. Branches of these nerves innervate at least two distinct anatomical subvolumes. However, the subvolumes of the ECRL defined by muscle architecture are not totally congruent with those defined by the innervation pattern. In the LG, the single muscle nerve branches into two main divisions, and these subsequently divide into branches which supply the three heads. However, each head does not receive a completely private nerve. These results indicate that human muscles are partitioned in a manner roughly similar to the divisions of the same muscles in cats and rats, but with less congruency of architecture and innervation.

Operant conditioning of spinal stretch reflexes in patients with spinal cord injuries

Hyperactive spinal stretch reflexes (SSRs) often occur with spinal cord injuries (SCI). These altered SSRs may impair movement. Recent studies in monkeys and human subjects have indicated that the magnitude of SSRs can be modulated using operant conditioning. The purpose of this study was to determine whether hyperactive biceps brachii SSRs could be operantly conditioned downward. Seventeen chronic (> 1 year postlesion) spinal cord-injured patients participated. Subjects were trained to keep biceps background (prestretch) electromyographic (EMG) activity and elbow angle at predetermined levels prior to having the elbow rapidly extended by a torque motor to elicit the biceps SSR. All subjects participated in six baseline sessions over a 2-week period. Then, subjects were randomly assigned to either control or training groups for the next 24 sessions over an 8-week period. By the end of the study, training subjects had significantly reduced biceps SSRs (t test, P < 0.001), while control subjects SSRs were not significantly reduced (t test, P > 0.05). The reduced SSRs persisted for up to 4 months following cessation of training. The results of this study support the hypothesis that hyperactive SSRs can be operantly conditioned downward in SCI patients.

Use of Imaging to Assess Normal and Adaptive Muscle Function

Physical therapists must be able to determine the activity and passive properties of the musculoskeletal system in order to accurately plan and evaluate therapeutic measures. Discussed in this article are imaging methods that not only allow for the measurement of muscle activity but also allow for the measurement of cellular processes and passive mechanical properties noninvasively and in vivo. The techniques reviewed are T1- and T2-weighted magnetic resonance (MR) imaging, MR spectroscopy, cine–phase-contrast MR imaging, MR elastography, and ultrasonography. At present, many of these approaches are expensive and not readily available in physical therapy clinics but can be found at medical centers. However, there are ways of using these techniques to provide important knowledge about muscle function. This article proposes creative ways in which to use these techniques as evaluative tools.

The prefrontal corticotectal projection in the cat

SummaryThe cells of origin and terminal distribution of the prefrontal corticotectal projection in the cat has been examined using retrograde cell-labeling with horseradish peroxidase (HRP) and anterograde axon-labeling with HRP or 3H-amino acid autoradiography. All prefrontal neurons labeled from unilateral enzyme deposits in the superior colliculus are pyramidal cells scattered through the thickness of layer V. The ipsilateral prefrontotectal neurons are located most densely in the banks and fundus of the presylvian sulcus and, to a lesser extent, in the anterior and frontal polar part of the gyrus proreus. About 10% as many cells are labeled in the contralateral prefrontal cortex in a similar distribution. Injections of HRP restricted to the superficial layers of the colliculus failed to label cells in the prefrontal cortex. Injections of HRP or 3H-proline-leucine in the region of these prefrontotectal neurons results in axonlabeling mainly, but not exclusively, in the ipsilateral superior colliculus where the labeled fibers are distributed in the layers below the stratum opticum. Labeled axons are especially dense in the intermediate gray layer where, caudally, they are arranged in two horizontally arrayed dorsal and ventral sheets interconnected by periodic columns of dense fiberlabeling interposed between columns of lesser fiberlabeling. Thus, the prefrontotectal projection of the cat here reported is consistent with that described earlier for the rat, but differs markedly from the primate in that prefrontal area 8 in monkeys projects also to the superficial tectal layers.

Contralateral and long latency effects of human biceps brachii stretch reflex conditioning

Results from previous studies on monkeys and human subjects have demonstrated that the biceps brachii spinal stretch reflex (SSR) can be operantly conditioned. The extent to which conditioning paradigms influence contralateral SSRs or longer latency responses in the same limb has not been examined. Nine subjects were given 10 training sessions to either increase or decrease the size of their biceps brachii SSR. Group changes were compared to the mean of six baseline (control) sessions. Both groups showed progressive SSR changes over the training sessions. Up-trained subjects increased their SSR responses by an average of 135.3% above baseline, with the last three sessions showing a 237.5% increase, while down-trained subjects reduced their average SSR responses by 43.4%, with a 52.7% reduction over the last three sessions. Ipsilateral longer latency responses showed average changes of 68.9% and-68.7% for up- and down-trainers, respectively. As in the case of SSRs, these responses changed progressively over sessions, with a 131.5% increase seen in the last three up-training sessions and an 82.4% reduction over the same period for down-trainers. Correlation coefficients between SSR and longer latency responses were high (R=0.90, up-trainers; R=0.87, down-trainers). Contralateral SSR and longer latency responses, measured in the absence of feedback and at least 10 min after ipsilateral conditioning, showed directional changes that were similar to the trained side, but their magnitudes were not as profound. Collectively, these data suggest that unilateral SSR conditioning affects spinal circuits controlling contralateral SSRs and influences longer latency responses.

Neuromuscular compartments in the human biceps brachii muscle.

Electrophysiological evidence suggests that the human biceps brachii muscle is organized into functional neuromuscular compartments. The purpose of this study was to determine whether there was an anatomical basis for these compartments. Dissection of the biceps revealed both architectural and nerve branching pattern compartmentalization within the muscle. Although the biceps brachii is grossly subdivided into long and short heads, these heads are further subdivided into roughly parallel architectural compartments. Moreover, these architectural compartments usually receive a private nerve branch, thus supporting the notion that the human biceps brachii has neuromuscular compartments.

Anatomical Partitioning of Three Human Forearm Muscles

Anatomical partitioning has been found in the human biceps brachii, extensor carpi radialis longus and flexor carpi radialis muscles. The purpose of this study was to determine if the human extensor carpi ulnaris, flexor carpi ulnaris and flexor digitorum profundus are anatomically partitioned. Evidence for or against anatomical partitioning was obtained by observation of the architectural and innervation characteristics of each of the investigated muscles. Twelve samples (11 were used for extensor carpi ulnaris) of each specific muscle type were harvested from perfused human cadavers. The architectural characteristics of tendinous boundaries, muscle fiber direction, and muscle fiber angle magnitude were observed, measured and documented. Microdissection technique was used to investigate the primary nerve branching pattern throughout each muscle. A primary nerve branch to a specific muscle region indicated possible partitioning by innervation. The extensor carpi ulnaris was found to have a variable number of primary nerve branches. The extensor carpi ulnaris may have four partitions by innervation alone or three congruent partitions by innervation and muscle fiber architecture. The nerve to the flexor carpi ulnaris clearly innervates two architectural partitions within the muscle. The innervation pattern to the flexor carpi ulnaris is congruent with muscle fiber architecture characteristics indicating consistent anatomical partitioning within the flexor carpi ulnaris. Two muscle nerves innervate the flexor digitorum profundus with branches innervating the medial and lateral regions of the muscle. Up to eight architectural partitions were found in a medial-to-lateral direction.

Plasticity in the Central Nervous System: Operant Conditioning of the Spinal Stretch Reflex.

Studies in monkey models have demonstrated that spinal stretch reflexes (SSRs) can be conditioned to be smaller or larger. Results of H-reflex conditioning studies further support the concept that operant conditioning alters the anatomical and biophysical properties of targeted alpha motoneurons. Results from able-bodied human subjects are strikingly similar to results from monkey models. Conditioning paradigms appear successful in downtraining the SSR of spinal-cord-injured patients who present with some residual control of a hyperactive biceps brachii. The conditioning may also affect movement control of spinal-cord-injured patients. Initial attempts at conditioning hyperactive SSRs of stroke patients have been equivocal. The site of lesion probably influences whether a stroke patient can successfully condition the SSR.

The relationship of extraneous movements to lumbar paraspinal muscle activity: Implications for EMG biofeedback training applications to low back pain patients

Within recent years clinicians and researchers have applied paraspinal EMG biofeedback procedures during static and dynamic movement retraining of chronic low back pain patients. Most of these applications make use of surface electromyography, an approach complicated by the fact that the erector spinae muscles are deeply situated. This descriptive study reveals that extraneous movements, such as neck flexion and pelvic rotation, can elicit profound activity from percutaneously placed EMG electrodes while little change is seen at the skin surface. The implications of these observations for the use of EMG feedback to remediate low back pain are discussed.