Main description:

Rarely have the many mechanisms that might underlie neural plasticity been examined as explicitly as they are in this broad, lavishly illustrated treatment of plasticity in the somatosensory system. The reader is provided with state-of-the-art knowledge of connections at all levels of the somatosensory system. The authors examine the propensity for changes of connectivity in both the mature and developing mammal and make clear proposals regarding the mechanisms underlying these changes. Their functional significance to relevant psychophysical and neurological observations is also discussed.

Contents:

1 Introductory Remarks.- 2 Plasticity in the Peripheral Somatosensory Nervous System.- 2.1 Aspects of Plasticity in the Peripheral Nervous System.- 2.2 Survival and Loss of Sensory Neurons After Lesions of the Peripheral Nervous System.- 2.2.1 Effect of Crush or Transection of Peripheral Nerve on Neurons of Sensory Ganglia.- 2.2.2 Trophic Dependence of Immature Sensory Neurons on the Periphery.- 2.2.3 Effect of Peripheral Nerve Transection on Different Types of Sensory Neurons in Dorsal Root Ganglia.- 2.2.4 Effect of Peripheral Nerve Section on Fibre Composition of Dorsal Roots.- 2.2.5 Fate of the Lost neurons.- 2.2.6 Sensory Cell Loss After Chemical Lesions of Afferent Fibres.- 2.3 Collateral Sprouting of Primary Afferent Fibres in the Periphery.- 2.3.1 Collateral Reinnervation of the Skin in Adult Mammals.- 2.3.2 Collateral Sprouting in Neonates.- 2.3.3 Effect of Neural Activity on Collateral Sprouting.- 2.3.4 Collateral Sprouting of Trigeminal Afferents.- 2.3.5 Collateral Sprouting and Sensory Recovery in Man.- 2.3.6 Fate of Collateral Sprouts After Regeneration of Original Nerve.- 2.4 Regeneration of Somatic Sensory Afferent Fibres.- 2.4.1 Numbers of Axons in Nerves Regenerating After Crush or Transection.- 2.4.2 Size of Regenerated Axons.- 2.4.3 Effect of Denervation on Specialized Cutaneous Mechanoreceptors.- 2.4.4 Reinnervation of Cutaneous Receptors by Regenerating Sensory Fibres.- 2.5 Modality Specificity of Somatosensory Nerve Regeneration.- 2.5.1 Regeneration of Myelinated Afferent Fibres to Hairy Skin.- 2.5.2 Regeneration of Myelinated Afferent Fibres to Glabrous Skin.- 2.5.3 Regeneration of Unmyelinated Afferent Fibres..- 2.6 Major Conclusions.- 3 Plasticity and the Mystacial Vibrissae of Rodents.- 3.1 General Account of Pathway.- 3.2 Normal Development of the Vibrissae and Their Neural Connections to the Cerebral Cortex.- 3.3 Effects of Lesions and Manipulations in Prenatal, Neonatal and Developing Animals.- 3.3.1 Damage of the Infraorbital Nerve.- 3.3.2 Lesions to One or More Vibrissae.- 3.3.3 The Effects of Supernumerary Vibrissae.- 3.3.4 The Effects of Lesioning Unmyelinated Afferents.- 3.3.5 Hyper- and Hypostimulation of Vibrissa Afferents.- 3.3.6 Cortical Alterations.- 3.4 Plasticity in the Vibrissa System of Adult Animals.- 3.4.1 The SI Cortex.- 3.4.2 The Ventral Posterior Medial Nucleus.- 3.5 Major Conclusions.- 4 Plasticity and the Spinal Dorsal Horn (with Notes on Homologous Regions of the Trigeminal Nuclei).- 4.1 Experimental Strategies for Demonstration of Plasticity in the Dorsal Horn of the Spinal Cord and Trigeminal Nuclei.- 4.2 Overview of Dorsal Horn Organization.- 4.2.1 Laminar Cytoarchitectonic Organization.- 4.2.2 Laminar Organization of the Termination of Primary Afferent Fibres.- 4.2.3 Microanatomical Organization of Low-Threshold Cutaneous Afferents.- 4.2.4 Relation of Functional Properties to Lamination of the Dorsal Horn.- 4.2.5 Inhibitory Receptive Fields.- 4.3 Somatotopic Organization of the Dorsal Horn.- 4.3.1 Dorsal Horn Neurons.- 4.3.2 Somatotopy and Lamination.- 4.3.3 Relation of Primary Afferent Projections to Dorsal Horn Somatotopy.- 4.3.4 Relation Between Dorsal Horn Cell Dendritic Morphology and Receptive Field.- 4.4 Effect of Lesions on Somatotopic Organization.- 4.4.1 Dorsal Rhizotomy.- 4.4.2 Chronic Spinal Lesions.- 4.4.3 Peripheral Nerve Transection or Crush.- 4.5 Mechanisms Underlying the Somatotopic Reorganization of Dorsal Horn Neurons.- 4.5.1 Physiological and Pharmacological Evidence for the Existence of Normally Ineffective.- Afferent Connections.- 4.5.2 Spontaneous Changes of Receptive Fields.- 4.5.3 Plasticity of Receptive Fields Induced by Afferent Activity.- 4.5.4 Involvement of Unmyelinated Afferents in the Somatotopic Reorganization After Peripheral Nerve Injury.- 4.5.5 Sprouting of Primary Afferent Fibres and Other Neurons as a Basis for Somatotopic Reorganization.- 4.6 Plasticity of the Developing Dorsal Hor.- 4.6.1 Development of Dorsal Horn Neurons and Primary Afferents.- 4.6.2 Functional Plasticity in Development.- 4.6.3 Somatotopic Reorganization Following Neonatal Peripheral Nerve Lesions.- 4.6.4 Anatomical Plasticity of Neonatal Afferent Projections.- 4.7 Major Conclusions.- 5 Plasticity and the Dorsal Column Nuclei.- 5.1 Advantages of the Dorsal Column Nuclei for Studies of Plasticity.- 5.2 Organization of the Dorsal Column Nuclei.- 5.2.1 Cytoarchitectonics.- 5.2.2 Ascending Afferent Pathways.- 5.2.3 Responses of Neurons to Natural Stimulation.- 5.2.4 Core and Shell Organization.- 5.2.5 Somatotopic Organization.- 5.3 Alterations of Inputs to the Nuclei.- 5.3.1 Section of Ascending Pathways.- 5.3.2 Effects of Dorsal Rhizotomy.- 5.3.3 Peripheral Nerve Section.- 5.4 Evidence for Ineffective Afferent Connections.- 5.4.1 Projections of Dorsal Roots and Peripheral Nerves.- 5.4.2 Projections of Single Afferent Fibres.- 5.4.3 Dendritic Spread of Cuneate Neurons.- 5.4.4 Electrical Stimulation and Widefield Neurons..- 5.4.5 Pharmacological Alterations of Receptive Fields.- 5.5 Recovery from Sensorimotor Deficits Following Dorsal Column Lesions.- 5.6 Plasticity of the DCN During Development.- 5.6.1 Effects of Prenatal Lesions.- 5.6.2 Effect of Neonatal Destruction of Unmyelinated Afferents.- 5.7 Major Conclusions.- 6 Plasticity and the Somatosensory Thalamus.- 6.1 Experimental Strategies and Plasticity in the Ventral Posterior Nuclei of the Thalamus.- 6.2 Anatomical Organization of Inputs and Outputs of the Ventral Posterior Nuclei.- 6.2.1 Primate and Cat.- 6.2.2 Raccoon.- 6.2.3 Rat.- 6.3 Responses of Neurons to Cutaneous Stimulation and the Effects of Anaesthetics and Other Drugs.- 6.4 Somatotopic Organization of the VPL and VPM.- 6.5 Effects of Alteration of Input on Somatotopic Organization.- 6.5.1 Reversible Blockade of Afferents and the Immediate Expression of New Inputs.- 6.5.2 Chronic Lesion of Afferent Pathways and Sprouting of Thalamic Afferents.- 6.6 Major Conclusions.- 7 Plasticity and the Somatosensory Cerebral Cortex.- 7.1 Experimental Strategies and Cortical Plasticity..- 7.2 Plasticity in the Cortex of Adult and Developing Primates.- 7.2.1 Multiple Representations.- 7.2.2 Thalamic Input and Intracortical Connectivity..- 7.2.3 Responses of Cortical Neurons to Natural Stimulation.- 7.2.4 Somatotopic Representation of the Hand in Areas 3b and 1.- 7.2.5 Anatomy and Innervation of the Monkey Hand.- 7.2.6 Anaesthetics and the Representation of the Hand.- 7.2.7 Injury and Subsequent Regeneration of Peripheral Nerves.- 7.2.8 Section and Ligation of Peripheral Nerves.- 7.2.9 Effects of Repeated Stimulation on Cortical Representations.- 7.2.10 Cortical Damage.- 7.3 Plasticity in the Cortex of Adult and Developing Cats.- 7.3.1 Somatotopic Organization, Cytoarchitectonics and Neuronal Responses.- 7.3.2 Thalamic Input and Ineffective Thalamocortical Connections.- 7.3.3 Effects of Anaesthetics and Other Drugs.- 7.3.4 Cordotomy and Section of Ascending Tracts.- 7.3.5 Blockage of Primary Afferent Input in Specific Dorsal Roots.- 7.3.6 Damage to Peripheral Nerves and Effects of Usage on Cortical Representation.- 7.3.7 Cortical Damage.- 7.4 Plasticity in the Cortex of Adult and Infant Raccoons.- 7.4.1 Somatotopic Organization and Cytoarchitectonics.- 7.4.2 Neuronal Responses in SI Cortex and the Effects of Anaesthetics.- 7.4.3 Ineffective Afferent Connections.- 7.4.4 Effects of Amputation on Cortical Somatotopy..- 7.5 Plasticity in the Cortex of Adult and Developing Rodents.- 7.5.1 Somatotopic Organization and Cytoarchitectonics.- 7.5.2 Section and Ligation of Peripheral Nerves in the Adult.- 7.5.3 Effects of Perinatal Nerve Section or Limb Amputation.- 7.5.4 Pharmacological Mechanisms Underlying Somatotopic Reorganization.- 7.5.5 Cortical Damage.- 7.6 Major Conclusions.- 8 Concluding Remarks.- 8.1 Plasticity During Development.- 8.1.1 Disruption of a Growing System and the Influence of the Periphery.- 8.1.2 The Influence of Afferent Axons and the Target Tissue.- 8.2 Evaluation of Experimentally Induced Plasticity in Adult Animals.- 8.2.1 Plasticity in the Peripheral Nervous System.- 8.2.2 Somatotopic Organization in Intact Animals as a Baseline for Assessing Altered Connections.- 8.2.3 Somatotopic-Artifacts in Regions Deprived of Their Normal Input.- 8.2.4 Plasticity and the Level of the Neuraxis.- 8.3 The Case for Ineffective Connections.- 8.3.1 Elucidation of Sub-Threshold Inputs.- 8.3.2 Somatotopically Inappropriate Projections of Afferent Axons.- 8.4 Spatial Extent of Immediate and Long-Term Changes in Somatotopic Organization.- 8.4.1 Distance Limits of Somatotopic Reorganization.- 8.4.2 Sprouting and Synaptogenesis in the Mature System.- 8.4.3 Recovery of Function.- 8.5 Normal Physiological Mechanisms and Plasticity.- 8.5.1 Inhibitory Receptive Fields and Partial Deafferentation.- 8.5.2 Neurotransmitters and Neural Systems That Regulate Sensory Input.- 8.6 Role of Plasticity in the Mature Somatosensory System.- References.