The Circuitry of the Human Spinal Cord: Its Role in Motor Control and Movement Disorders

Half-title......Page 2
Title......Page 4
Copyright......Page 5
Contents......Page 6
Preface......Page 16
Acknowledgements......Page 20
Abbreviations......Page 22
Animal studies......Page 24
The H reflex, tendon jerk and short-latency spinal stretch reflex......Page 25
The orderly recruitment of motoneurones in the monosynaptic reflex......Page 26
Awareness......Page 27
Recording......Page 28
Unipolar and bipolar stimulation......Page 29
Maximal M wave (Mmax)......Page 30
Tendon jerk......Page 31
Motoneurones do not discharge at the same time in the test reflex......Page 32
The recovery cycle of the H reflex......Page 33
Limitations related to mechanisms acting on the afferent volley of the reflex......Page 34
Alterations in the excitability of Ia afferents......Page 35
Post-activation depression......Page 36
Disynaptic limitation of the group Ia excitation......Page 37
Can the results obtained for the quadriceps be generalised?......Page 38
Sensitivity of reflexes of different size to facilitation and inhibition......Page 39
Input—output relationship within the motoneurone pool......Page 40
Definition......Page 41
Change in the slope of the input—output relationship......Page 42
Latency......Page 43
Antidromic re-excitation of motoneurones......Page 44
Variability and persistence......Page 45
Comparison of the H and F responses......Page 46
Basic methodology......Page 47
Estimate of the central delay......Page 48
Inhibition of the motoneurone pool......Page 49
Ease and rapidity of the experiment......Page 50
Post-stimulus time histograms (PSTHs) of the discharge of single motor units......Page 51
Basic methodology......Page 52
How to isolate one motor unit?......Page 53
Stimuli delivered randomly......Page 54
Estimation of the latency of a change in discharge probability......Page 55
CUSUM......Page 56
When stimulation is triggered by the previous discharge......Page 57
Normalisation of the results......Page 58
Voluntary activation......Page 59
Stimulation......Page 60
Significance of changes in CFS produced by conditioning stimuli......Page 61
Surface electrodes are not selective......Page 62
Multiple descending volleys elicited by cortical stimulation......Page 63
Stimulation using different coils......Page 65
Responses in leg muscles......Page 66
Motoneurones responsible for the MEP......Page 67
Convergence of excitation and inhibition onto common interneurones......Page 68
Summation of EPSPs......Page 69
Limitations......Page 70
Coherence techniques......Page 71
Initial studies......Page 72
Basic methodology......Page 73
'Pool problems'......Page 74
Characteristics......Page 75
Recording......Page 76
The CFS size......Page 77
Critique: advantages, limitations, conclusions......Page 78
REFERENCES......Page 79
Phylogenetic adaptation of reflex pathways......Page 86
Ia afferents......Page 87
Hindlimb......Page 88
Soleus H reflex......Page 89
Low electrical threshold......Page 90
Homonymous peak in the PSTHs of single motor units......Page 92
Principle of the procedure......Page 93
Critique......Page 95
Evidence that monosynaptic heteronymous excitation is Ia in origin......Page 96
Tendon tap......Page 98
Effects of long-lasting tendon vibration......Page 99
Growth of heteronymous Ia monosynaptic excitation......Page 100
Conclusions......Page 101
Preferential distribution of the monosynaptic Ia input to small motoneurones......Page 102
Connections between close synergists operating at the same joint......Page 104
Connections linking ankle muscles that are not close synergists......Page 105
Connections between close synergists......Page 106
Absence of proximal-to-distal projections......Page 107
Distal-to-proximal connections......Page 108
Ia excitation of antagonists in adults?......Page 109
Hopping......Page 110
Landing......Page 111
Standing......Page 112
History of the long-latency reflexes in humans......Page 113
Origin of long-latency stretch reflexes in different muscles......Page 114
Heteronymous monosynaptic Ia excitation......Page 115
Running, hopping and landing......Page 116
Ia projections from intrinsic hand muscles......Page 117
Comparison with F wave studies......Page 118
Background from animal experiments......Page 119
Depression at rest......Page 120
Post-activation depression and pathophysiology of spasticity......Page 122
The short-latency spinal stretch reflex......Page 123
Background from animal experiments......Page 124
Bidirectional connections......Page 125
Upper limb......Page 126
Heteronymous monosynaptic Ia excitation......Page 127
Peripheral neuropathies, mononeuropathies and nerve lesions......Page 128
REFERENCES......Page 129
Initial investigations......Page 136
Gamma innervation......Page 137
Morphological differences between feline and human spindles......Page 138
Tendon jerk......Page 140
Underlying principle......Page 141
Basic methodology......Page 142
Identification......Page 143
Uncertainties of the technique......Page 146
Thixotropy in human investigations......Page 147
Perspectives......Page 148
Thixotropy......Page 149
Lower limb......Page 150
Relaxed forearm extensor muscles......Page 152
Tendon organs......Page 153
Reflex reinforcement by remote muscle contraction: the Jendrassik manoeuvre......Page 154
Spindle acceleration after the onset of EMG......Page 156
Fusimotor activity when reliant on proprioceptive feedback during standing......Page 158
Necessity for afferent feedback......Page 159
Hand and forearm muscles......Page 160
Studies in patients and clinical implications......Page 161
Absence of alpha/gamma co-activation in clonus......Page 162
Rigidity......Page 163
Gamma efferent activation by corticospinal drives......Page 164
Acceptable methods......Page 165
Effects of cutaneous afferents on fusimotor neurones......Page 166
Effects of voluntary effort on fusimotor drive to the contracting muscle......Page 167
REFERENCES......Page 168
Pharmacology......Page 174
Input from alpha motoneurones......Page 175
Projections to gamma motoneurones......Page 176
This interpretation is erroneous......Page 177
Conditioning and test reflexes......Page 178
Possible role of AHP......Page 180
Pharmacological validation......Page 182
Limitations......Page 183
Underlying principles......Page 184
Inhibition elicited by an antidromic motor volley......Page 185
Arguments for recurrent inhibition......Page 189
Arguments against other mechanisms......Page 190
Limitations......Page 191
Strength and distribution of heteronymous recurrent inhibition in the lower limb......Page 192
Pattern of distribution......Page 193
Absence of recurrent inhibition of reciprocal inhibition at wrist level......Page 194
Methodology......Page 196
Changes prior to contraction......Page 197
Effects of the voluntary motor discharge......Page 199
Changes in heteronymous recurrent inhibition during voluntary contractions......Page 201
The gain hypothesis......Page 202
Depression of the H' test reflex......Page 203
Functional implications......Page 204
Functional implications......Page 206
Patients with amyotrophic lateral sclerosis......Page 207
Changes in homonymous recurrent inhibition during motor tasks in spastic patients......Page 209
Changes in recurrent inhibition in normal motor control......Page 210
Underlying principles, conditioning and test reflexes......Page 211
Underlying principle......Page 212
TMS suppresses homonymous and heteronymous recurrent inhibition......Page 213
Flexion—extension......Page 214
REFERENCES......Page 215
Initial findings......Page 220
Pharmacology......Page 221
Flexion reflex afferents (FRA)......Page 222
Presynaptic inhibition......Page 223
Monosynaptic test reflex......Page 224
Modulation of the on-going EMG......Page 226
Tendon tap......Page 227
Recurrent inhibition of the relevant interneurones......Page 228
Evidence for recurrent depression of reciprocal Ia inhibition from ankle extensors to tibialis anterior......Page 229
Intensity of the conditioning volley......Page 231
Reciprocal Ia inhibition between flexors and extensors of the ankle......Page 232
Reciprocal Ia inhibition between flexors and extensors of the knee......Page 233
Inhibition at wrist level does not fulfil the criteria for reciprocal Ia inhibition......Page 234
Post-activation depression......Page 235
Cutaneous facilitation of reciprocal Ia inhibition......Page 237
Descending facilitation of reciprocal Ia inhibition......Page 238
Vestibulospinal facilitation of reciprocal Ia inhibition......Page 239
Neuronal pathways......Page 240
Individual variations......Page 242
Presynaptic inhibition......Page 243
Effects due to the 'natural' Ia discharge......Page 244
Mechanisms underlying an increase in natural reciprocal Ia inhibition during voluntary contraction......Page 245
Mutual inhibition of 'opposite' Ia interneurones......Page 246
Mechanisms underlying the decreased reciprocal Ia inhibition during co-contraction......Page 248
Methodology......Page 250
Peroneal-induced reciprocal Ia inhibition of soleus motoneurones......Page 252
The early facilitation that often replaces the early inhibition could be due to Ib excitation......Page 253
Changes during voluntary contraction......Page 254
Evidence for plasticity in the pathway of reciprocal Ia inhibition......Page 255
At rest......Page 256
Role of reciprocal Ia inhibition in motor tasks......Page 257
Elicitation by Ia volleys......Page 258
Wrist level......Page 259
Voluntary activation of the agonistic muscle......Page 260
During voluntary dorsiflexion......Page 261
REFERENCES......Page 262
Initial findings......Page 267
Absence of inhibitory projections from Renshaw cells to Ib interneurones......Page 268
Ascending tract neurones......Page 269
Peripheral afferents......Page 270
Reflex reversal during fictive locomotion......Page 271
Inhibition in the PSTHs of single units......Page 272
Effects of tendon taps......Page 275
PSTHs of single units......Page 276
Biphasic effects and presynaptic inhibition of Ia terminals......Page 278
Homonymous Ib inhibition......Page 279
Convergence of Ib afferents from different muscles......Page 280
Common peroneal effects on quadriceps motoneurones......Page 281
Use of presynaptic inhibition of Ia terminals......Page 283
Cutaneous suppression of Ib inhibition to knee muscles at rest......Page 284
Conclusions......Page 285
Conclusions......Page 286
Weak contractions......Page 288
Motor tasks and physiological implications......Page 290
Decrease in Ib inhibition or decrease in presynaptic inhibition of Ia terminals?......Page 291
A descending post-synaptic mechanism?......Page 293
Cutaneous facilitation......Page 294
Ib inhibition from contracting muscles to inactive synergists......Page 295
Different roles of the triceps surae in quadrupedal and bipedal locomotion......Page 296
Functional implications......Page 297
Methodology......Page 298
Parkinson's disease......Page 299
Increased group facilitation or decreased reciprocal Ia inhibition?......Page 300
Contribution to pathophysiology of spasticity......Page 301
Background from animal experiments......Page 302
Ib inhibition......Page 303
Suppression of Ib inhibition to voluntarily activated motoneurones......Page 304
Ib inhibition......Page 305
REFERENCES......Page 306
Initial findings......Page 311
Group II interneurones......Page 312
Conclusions......Page 313
Other peripheral afferents......Page 314
Post-activation depression......Page 315
Late high-threshold facilitation of the H reflex......Page 316
 PSTHs......Page 318
Electrically induced responses......Page 320
Contamination by group I effects......Page 322
Electrically induced group II excitation......Page 324
Heteronymous group II excitation from leg muscles to thigh motoneurones......Page 325
Rostral location of the interneurones mediating group II excitation......Page 326
Heteronymous group II excitation......Page 327
Absence of direct evidence......Page 328
Absence of evidence for cutaneous projections......Page 329
Corticospinal facilitation of group II excitation......Page 330
Voluntary contraction of the quadriceps......Page 333
Role of homonymous group II pathways in transient perturbations of stance......Page 335
Peroneal group II facilitation of quadriceps......Page 336
Changes in group II excitation during gait......Page 337
Suppression of the EMG activity by unloading......Page 338
Further evidence for group II excitation......Page 339
Possible underlying mechanisms and functional implications......Page 341
Conclusions......Page 342
Deep peroneal-induced heteronymous facilitation of the quadriceps H reflex......Page 343
Monoaminergic gating......Page 344
Stroke patients......Page 345
Exaggerated stretch reflexes are strongly depressed by clonidine and tizanidine......Page 347
Conclusions......Page 348
Role of group II pathways in natural motor tasks......Page 349
Underlying principles......Page 351
Conclusions......Page 352
Inhibition of excitatory effects......Page 353
Peripheral neuropathies......Page 354
REFERENCES......Page 355
Mechanisms......Page 360
Electrophysiology......Page 361
Selectivity of the control of presynaptic inhibition......Page 362
Underlying principle......Page 363
Short vibration of a heteronymous tendon......Page 364
Electrically induced 'D1' and 'D2' inhibitions......Page 366
Occlusion......Page 367
Underlying principle......Page 368
Techniques using single motor units......Page 369
Projections on Ia terminals directed to different motoneurone types......Page 370
Excitation from group I afferents......Page 371
Facilitation of heteronymous excitation......Page 373
Data for single units......Page 374
Tonic level of presynaptic inhibition of Ia terminals......Page 376
Possible mechanisms and functional significance......Page 377
Changes in presynaptic inhibition during various contractions......Page 378
Origin......Page 381
Functional implications......Page 382
Selective contraction of the antagonistic muscle......Page 383
Presynaptic inhibition of Ia terminals during contraction of remote muscles......Page 384
Changes in presynaptic inhibition of Ia terminals on upper limb motoneurones......Page 385
Investigations using the soleus H reflex......Page 386
Functional implications......Page 387
Changes in D1 and D2 inhibition......Page 388
Functional implications......Page 389
Clinical studies......Page 390
Lower limb......Page 391
Cerebral lesions......Page 392
Changes in presynaptic inhibition during gait......Page 393
Decreased presynaptic inhibition of FCR Ia terminals......Page 394
Role of changes in presynaptic inhibition of Ia terminals in normal motor control......Page 395
Background from animal experiments......Page 396
Routine studies......Page 397
Organisation and pattern of connections......Page 398
Ia terminals on motoneurones of inactive synergistic muscles of the lower limb......Page 399
Stroke patients......Page 400
REFERENCES......Page 401
Short-latency FRA responses......Page 407
The toe extensor reflex of the cat......Page 408
Projections to motoneurones innervating slow- and fast-twitch motor units......Page 410
Grouping FRA together......Page 411
Convergence of nociceptive afferents on FRA interneurones......Page 412
There is inhibition of pathways mediating long-latency FRA reflexes by pathways mediating short-latency FRA reflexes......Page 413
Electrical stimuli to cutaneous nerves......Page 414
Plantar responses......Page 415
The RII response elicited in the short head of the biceps femoris by stimulation of the sural nerve......Page 417
Radiant heat......Page 419
Recordings of single units......Page 421
Stimuli delivered to the skin......Page 422
The central delay of the withdrawal reflexes of the limbs is less well defined......Page 423
Functional organisation of early  withdrawal reflexes......Page 424
Functional organisation with respect to the receptive field......Page 425
Receptive fields for individual muscles......Page 427
Withdrawal responses elicited at rest......Page 428
Long-latency flexor reflexes......Page 430
Stimulation of contralateral high-threshold cutaneous afferents depresses the late ipsilateral flexor reflex......Page 431
Plasticity of late responses......Page 433
Depression by tactile cutaneous volleys......Page 434
Nociceptive inhibition of the soleus H reflex......Page 435
Modulation of the on-going EMG......Page 437
Upper limb......Page 438
RII responses evoked at rest......Page 441
RII reflex......Page 442
Conclusions......Page 443
Latencies of late responses are compatible with a transcortical pathway......Page 444
Alternative possibilities to transcortical pathways......Page 446
First dorsal interosseous (FDI) conditioned by electrical stimuli......Page 447
Functional implications......Page 448
Task-related changes in cutaneomuscular responses......Page 450
Functional implications......Page 451
Task-related changes in cutaneomuscular responses......Page 452
Evidence for a transcortical response......Page 453
Changes in patients and clinical implications......Page 455
The Babinski response......Page 456
Flexor spasms......Page 457
Withdrawal reflexes in the upper limb......Page 458
Withdrawal reflexes......Page 459
Nociceptive reflexes may be of value in monitoring the effects of medication for pain......Page 460
Patients with complete spinal transection......Page 461
FRA pathways......Page 462
Modulation of motoneurone excitability......Page 463
Functional organisation of early withdrawal reflexes......Page 464
The different responses......Page 465
'Private' pathway or changes in transmission in another pathway?......Page 466
Complete spinal transection......Page 467
REFERENCES......Page 468
Multi-excitatory convergence onto propriospinal neurones......Page 475
Inhibitory mechanisms in the propriospinal system......Page 476
Scarcity and weakness of propriospinally mediated EPSPs under control conditions......Page 477
Underlying principles......Page 478
Limitations of the tests to study propriospinal excitation of upper limb motoneurones......Page 480
Cutaneous suppression of the on-going EMG......Page 481
Evidence for a rostral location of the relevant interneurones......Page 482
Weakness of the peripheral excitatory input......Page 483
Extra facilitation on combined stimulation......Page 484
Extra facilitation implies convergence onto common interneurones......Page 485
Inhibition of propriospinal neurones via feedback inhibitory interneurones......Page 486
Increasing TMS intensity results in a decrease in the peripheral extra facilitation of the corticospinal peak in all motor units tested......Page 487
Mechanisms underlying the reversal......Page 489
Activation of inhibitory interneurones......Page 490
Organisation in subsets with regard to the muscle afferent input......Page 491
Distribution in single motor units......Page 492
Suppression of the on-going ECR EMG while the H reflex is spared......Page 494
Cutaneous suppression of the corticospinal command to various motor nuclei......Page 496
Reflex facilitation at the onset of voluntary contraction......Page 497
Evidence for descending facilitation of propriospinal neurones......Page 498
Handedness-related asymmetry of propriospinal excitation during simple tasks......Page 499
Distribution to different types of motoneurones......Page 500
Corticospinal control of cutaneous suppression......Page 501
Modulation of the MEP in biceps and triceps brachii......Page 502
Asymmetrical EMG suppression......Page 504
Possible mechanisms underlying increased excitation of the propriospinal neurones during voluntary contraction......Page 506
Greater cutaneous suppression of the on-going EMG......Page 507
Stroke patients......Page 508
Limitations......Page 509
Peripheral inhibition of propriospinal neurones......Page 510
Evidence for propriospinal transmission of a part of the descending command......Page 511
Lesion of the spinal cord at the junction C6—C7 spinal level......Page 512
Initial studies......Page 513
Non-monosynaptic excitation of voluntarily activated single motor units......Page 514
Evidence for rostral location of the relevant interneurones......Page 516
Strength of the peroneal group I excitation to quadriceps......Page 517
Lateral inhibition between conditioning volleys applied to two different nerves......Page 519
Medium-latency reciprocal inhibition......Page 520
Which interneurones?......Page 521
Increased facilitation of the quadriceps H reflex during voluntary contraction......Page 523
Quadriceps contractions......Page 525
Patients with Parkinson's disease......Page 526
Peripheral excitation of lumbar propriospinal neurones......Page 528
REFERENCES......Page 529
11 Involvement of spinal pathways in different motor tasks......Page 534
Servo-assistance through group II pathways......Page 535
Changes in recurrent inhibition......Page 537
Afferent discharges accompanying a voluntary flexion—extension movement......Page 538
Propriospinally mediated excitation......Page 539
Control of mechanical features (force, speed)......Page 540
Recruitment of different types of motor units......Page 541
Longer-latency propriospinally mediated inhibition......Page 542
Onset of movement......Page 543
Elbow muscles......Page 544
The organisation of spinal circuits at wrist level differs from that at hinge joints in many aspects......Page 545
Is there descending facilitation of the pathway?......Page 547
Peripheral activation of the relevant interneurones......Page 548
Propriospinal pathways......Page 549
Hierarchical control schema......Page 550
Relaxation of antagonistic muscles......Page 551
Reaching: an example of hierarchical control......Page 552
Projections to ascending tracts......Page 553
Homonymous recurrent inhibition......Page 554
Presynaptic inhibition of Ia terminals......Page 555
Joint stiffness......Page 556
Stretch reflex......Page 557
Afferent cues from multiple sources......Page 558
Contrary arguments......Page 559
Unstable postural tasks requiring prolonged muscle contractions......Page 560
Responses to fast transient perturbations of stance......Page 561
Long-latency responses in the stretched muscle (M3)......Page 562
Monosynaptic Ia responses in triceps surae......Page 563
Muscles operating at joints other than ankle......Page 564
Peculiarities of human walking......Page 565
Conclusions......Page 567
Group II excitation......Page 568
Prevention of excessive reflex activity in triceps surae......Page 569
Reactions to external perturbations......Page 570
Long-latency responses......Page 571
Conclusions......Page 572
REFERENCES......Page 573
Spasticity......Page 579
Pathophysiology of spasticity varies with the causative lesion......Page 580
To what extent does spasticity contribute to motor impairment?......Page 581
Patients with spinal cord lesions......Page 582
Hyperexcitability of motoneurones......Page 583
Increased F waves......Page 585
Increased fusimotor activity......Page 586
Recordings from spindle afferents......Page 587
Suppression of the H reflex by a heteronymous group I volley......Page 588
Increased oligosynaptic propriospinally mediated group I excitation......Page 589
Methodology......Page 590
Change in Ib inhibition or in group I excitation?......Page 591
Conclusions......Page 592
Several spinal mechanisms probably contribute to spasticity......Page 593
Plastic changes......Page 594
Changes in the intrinsic properties of muscle fibres (contracture)......Page 595
Changes in spinal pathways during movements in spasticity......Page 596
Reciprocal inhibition......Page 597
Exaggeration of stretch reflexes in stroke patients......Page 598
Presynaptic inhibition on Ia terminals......Page 599
Abnormal transmission in some pathways......Page 600
Spasticity in cerebral palsy......Page 602
Post-activation depression......Page 603
From spinal shock to spasticity......Page 604
Changes in viscoelastic properties of muscle fibres......Page 605
Origin of the increased long-latency stretch reflex response......Page 606
Hmax/Mmax ratio......Page 607
Conclusions......Page 608
Ia terminals to soleus motoneurones......Page 609
Conclusions......Page 610
Evidence for increased group II excitation......Page 611
Responses produced by tilt of the platform......Page 612
Reciprocal Ia inhibition at ankle level......Page 613
Increased propriospinal transmission......Page 614
REFERENCES......Page 615
Index......Page 624