Progress in the neural sciences in the the century after Cajal (and the mysteries that remain)

One, no-one and a hundred thousand brains: J.C. Eccles, J.Z. Young and the establishment of the neurosciences (1930s-1960s)

Contemporary neurosciences have grown beyond the limits of a natural science. To its most vocal advocates, the study of the human brain can provide nothing short of the basis for a new science of man-the link between the "natural" and "human" sciences-as a simple consequence of the growing mass of facts relating to this most marvelous organ, accumulated in the last four decades. This straightforward picture of the growing import of the neurosciences simplifies and obscures the myriad different interpretations and images of "the brain" that have inspired the development of the neurosciences. Among them, this chapter will consider two deeply contrasting early images of the brain: the cellular-physiological brain proposed since the 1950s by John Carew Eccles, and the model-"whole" brain championed by John Zachary Young. Eccles' program was focused on the vertebrate synapse, and Young's on the whole brain of an "advanced" invertebrate (the octopus). The former was the programmatic extension of a long neurophysiological tradition, and the latter an outspoken attempt at providing a revolutionary model for the organization of an unprecedented research effort. One underscored continuity and scientific "soundness," and the other promised rupture and new, imaginative solutions to age-old problems. Nevertheless, they have been later lumped together into a single, marvelous and progressive history, or mythology, of the Science of the Brain. This chapter will show how the organizing principle of these two opposed (if almost equally successful) research efforts was not the foggy, ever-changing image of an experimental brain-in-becoming, but the clear, fixed horizon of a promised brain.

A Theory of Consciousness

Consciousness is the subjective awareness of momentary experience interpreted in the context of personal memory and present state. I propose that two brain systems converge to create consciousness. The exogenous system sends information about multimodal external stimuli to basal dendrites in widely dispersed pyramidal cell ensembles in the cortex of the brain; this system produces synchronized fragments of sensations. The endogenous system distributes readout of representations of memories, activated in systems established by associative learning, diffusely to apical dendrites. Convergence of exogenous and endogenous inputs enhances cellular excitability, and fragmented sensations are thereby converted to fragments of perception. Local field potentials periodically modulate all cortical membrane potentials and facilitate synchronous discharge of these excited elements. Feedback between the cortex and the thalamus results in a cortico-thalamo-cortical reverberation, binding the fragments into a unified global percept. Sustained reverberation produces a resonating electromagnetic field of synchronized elements. The momentary content of information in the brain is this distributed coherence, which is negative entropy. Consciousness is a physical property of this field, producing the subjective awareness of this information.

Knee kinematics and kinetics in former soccer players with a 16-year-old ACL injury--the effects of twelve weeks of knee-specific training

Background

Training of neuromuscular control has become increasingly important and plays a major role in rehabilitation of subjects with an injury to the anterior cruciate ligament (ACL). Little is known, however, of the influence of this training on knee stiffness during loading. Increased knee stiffness occurs as a loading strategy of ACL-injured subjects and is associated with increased joint contact forces. Increased or altered joint loads contribute to the development of osteoarthritis.

The aim of the study was to determine if knee stiffness, defined by changes in knee kinetics and kinematics of gait, step activity and cross-over hop could be reduced through a knee-specific 12-week training programme.

Methods

A 3-dimensional motion analysis system (VICON) and a force plate (AMTI) were used to calculate knee kinetics and kinematics before and after 12 weeks of knee-specific training in 12 males recruited from a cohort with ACL injury 16 years earlier. Twelve uninjured males matched for age, sex, BMI and activity level served as a reference group. Self-reported patient-relevant data were obtained by the KOOS questionnaire.

Results

There were no significant changes in knee stiffness during gait and step activity after training. For the cross-over hop, increased peak knee flexion during landing (from 44 to 48 degrees, p = 0.031) and increased internal knee extensor moment (1.28 to 1.55 Nm/kg, p = 0.017) were seen after training, indicating reduced knee stiffness. The KOOS sport and recreation score improved from 70 to 77 (p = 0.005) and was significantly correlated with the changes in knee flexion during landing for the cross-over hop (r = 0.6, p = 0.039).

Conclusion

Knee-specific training improved lower extremity kinetics and kinematics, indicating reduced knee stiffness during demanding hop activity. Self-reported sport and recreational function correlated positively with the biomechanical changes supporting a clinical importance of the findings. Further studies are needed to confirm these results in women and in other ACL injured populations.