How Brain-like is the Spinal Cord?
Interacting Cell Assemblies in the Nervous System
Published on 12. February 1988
Book
Hardback
XVIII, 334 pages
978-3-540-18405-8 (ISBN)
Description
"Theorizing about brain functions is often considered slightly disreputable and anyhow a waste of time -perhaps even 'philoso- ical'" 1 P. S. CHURCHLAND At present there are no unanimously accepted general con cepts of brain operation and function. This is especially the case with regard to so-called "higher" functions such as per ception, memory or the coupling between sensory input and motor output. There are a number of different reasons for this. Some may be related to experimental limitations allowing the simultaneous recording of the activities of only a restricted number of neurones. But there are also conceptual difficulties hindering the transition from "single-neurone" schemes, in which neurones are assigned relatively specific tasks (such as feature detection), to more complex schemes of nerve cell as semblies (for a discussion of some of the difficulties see Abeles 1982; von der Malsburg 1981; Kriiger 1983). Whilst much is known about the basic properties and functions of single neu rones, whose operations we hope to understand in the foresee able future, this does not hold true in the same way for the working of large assemblies of neurones.
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Content
1 Correlations Between Spike Trains of Supraspinal Neurones.- 1.1 Correlations Between Discharge Patterns of Cortical Neurones.- 1.2 The Basic Method of Cross-Correlating Spike Trains.- 1.3 Correlations Between Discharge Patterns of Cortical Neurones and Their Role in Some Recent Models of Brain function.- 1.3.1 Synfire Chains.- 1.3.2 A Correlation Theory of Brain Function: Synaptic Modulation.- 1.3.3 Synaptic Plasticity.- 1.3.4 Summary.- 1.4 Brainstem.- 1.4.1 A Spatio-Temporal Cross-Correlation Model for Acoustic Pitch Detection.- 1.4.2 Activity Patterns in the Reticular Formation.- 1.4.3 Summary.- 2 Correlations Between Spinal Neurones.- 2.1 Correlations Between ?-Motoneurone Discharges.- 2.1.1 Types of Correlation Between ?-Motoneurone Discharges.- 2.1.2 Causes of ?-Motoneurone Correlations.- 2.2 Correlations Between ?-Motoneurone Discharges.- 2.3 Correlations Between ?-Motoneurone Discharges.- 2.3.1 Types of Correlation Between ?-Motoneurone Discharges.- 2.3.2 Causes of ?-Motoneurone Correlations.- 2.3.3 Correlations Between ?- and ?-Motoneurone Discharges.- 2.4 Summary.- 2.5 Correlations Between Muscle Afferent Discharges.- 2.5.1 Correlations Between Ia Afferent Discharges in Decerebrate Cats.- 2.5.2 Correlations Between Spindle Afferent Discharges Time-Related to Motor Unit Twitches.- 2.6 The Effect of Fusimotor Input on Spindle Afferent Correlations.- 2.7 Summary.- 2.8 Effects of Correlations Between Presynaptic Fibres on Spinal Neurones.- 2.8.1 An Introductory Model.- 2.8.2 Effects of Muscle Afferent Correlations on ?-Motoneurones: Monosynaptic Connexions.- 2.8.3 Summary.- 2.9 Interneuronal Circuits.- 2.9.1 Signal Transmission to Motoneurones Through Interneuronal Systems.- 2.9.2 Some Spinal Interneuronal Circuits Influencing Correlations.- 2.9.3 Summary.- 3 Tremor States.- 3.1 Frequency-Displacement Amplitude Relations for Normal Hand Tremor.- 3.2 Muscle Contraction as a Stochastic Process.- 3.2.1 The Basic Mechanism of Small-Amplitude Physiological Tremor.- 3.2.2 Nonlinearities of Motor Unit Behaviour.- 3.2.3 Effects of Motor Unit Contractions on Spindle Afferent Discharge.- 3.3 Localised Stretch Reflexes Acting as a Tremor-Suppressive Mechanism?.- 3.3.1 Muscles with "In-parallel" Structure and Their Monosynaptic Reflex Organisation.- 3.3.2 Muscles with "In-series" Structure and Their Monosynaptic Reflex Organisation.- 3.3.3 Summary and Limitations.- 3.4 Further Feedback Systems.- 3.4.1 Involvement of the Renshaw Cell System in Tremor.- 3.4.2 Multiple Meshed Feedback Loops.- 3.4.3 Remarks on the Possible Significance of Physiological Tremor.- 3.5 Plasticity in the Spinal Cord.- 3.6 Summary.- 4 Recurrent Inhibition and Proprioceptive Feedback.- 4.1 Fundamental Functions of the Spinal Cord.- 4.2 Specific Functions of Recurrent Inhibition and the Stretch Reflex.- 4.2.1 Functional Models of Renshaw Cell Inhibition.- 4.2.2 Functional Models of the Stretch Reflex.- 4.2.3 Summary.- 4.3 Structural and Functional Analogies Between Spinal Recurrent Inhibition and Proprioceptive Feedback.- 4.3.1 Spatial Organisation of Recurrent and Proprioceptive Feedback.- 4.3.2 Feedback of Different Functional Types of ?-Motoneurones.- 4.3.3 Static Input-Output Relations in the Pathways from Motor Axons to Renshaw Cells or Spindle Afferents.- 4.3.4 Dynamics of Signal Transmission from Motor Axons to Renshaw Cells or Spindle Afferents.- 4.3.5 Responses of ?-Motoneurones to Activation of Single Homonymous Motor Axons Mediated Through Renshaw Cells or Motor Units and Muscle Afferents.- 4.3.6 Differentiated Feedback?.- 4.3.7 Presynaptic Inhibition.- 4.3.8 Recurrent Inhibitory vs Proprioceptive Feedback on ?-Motoneurones.- 4.3.9 Recurrent Inhibition vs Ia Excitation of Reciprocal Ia Inhibitory Interneurones.- 4.3.10 Mutual Inhibition Between Renshaw Cells vs Reciprocal Inhibition.- 4.3.11 Supraspinal Inputs to ?-Motoneurones and Renshaw Cells.- 4.3.12 A Phylogenetic Comparison.- 4.3.13 Summary.- 4.4 The Reafference Principle.- 4.5 The Renshaw Cell System as an Efference Copy?.- 4.6 Model-Reference Control Systems.- 4.6.1 Basic Notions.- 4.6.2 Hypothetical Motor Control Schemes.- 4.7 Adaptive Control Systems.- 4.7.1 Basic Notions.- 4.7.2 Interpretations.- 4.8 An Integrated Model Including Proprioceptive Feedback and Recurrent Inhibition.- 4.9 Remarks on the Function of the Integrated System.- 4.10 Are the Inputs to ?-Motoneurones and Renshaw Cells Matched to Each Other?.- 4.11 Relation of Fusi- and Skeletomotor Activation Patterns: Task Dependence.- 4.12 ?-Motoneurones and Renshaw Cells as Integrative Centres.- 4.13 Suggestions for Further Research.- 4.14 Summary.- 5 Problems in Motor Control.- 5.1 On the Modules of Motor Control.- 5.1.1 Differential Activation of Muscle Compartments.- 5.1.2 Nonlinear Mechanical Interaction Between Muscle Compartments.- 5.1.3 Different Mechanical Output Actions of Muscle Compartments.- 5.1.4 Spatial Density Gradients for Different Types of Muscle Fibre.- 5.1.5 Muscle Fibre Architecture.- 5.1.6 Ontogeny.- 5.1.7 The Task Group Notion.- 5.2 The Problem of the Variable(s) Controlled in Motor Acts.- 5.3 Which Are the Measured Variables?.- 5.4 Spatial Transformations.- 5.5 Temporal Aspects.- 5.6 Multimodal Organisation of Spinal Neural Assemblies.- 5.7 Summary.- 5.8 Concluding Remarks.- Appendix A Auto- and Cross-Correlations.- Appendix B Cross-Correlations Between Three Spike Trains.- Appendix C Event-Related Cross-Correlations.- Appendix D Statistical Analysis of Nonlinear Physiological Systems.- Appendix E On Spurious Synchronisation of Two Semiregularly Firing Neurones.- Appendix F Spectral Analysis.- Appendix G A Remark on Correlation Patterns.- References.