Dispersed Activity during Passive Movement in the Globus Pallidus of the 1-Methyl-4-Phenyl-1,2,3,6-Tetrahydropyridine (MPTP)-Treated Primate

Parkinson's disease is a neurodegenerative disorder manifesting in debilitating motor symptoms. This disorder is characterized by abnormal activity throughout the cortico-basal ganglia loop at both the single neuron and network levels. Previous neurophysiological studies have suggested that the encoding of movement in the parkinsonian state involves correlated activity and synchronized firing patterns. In this study, we used multi-electrode recordings to directly explore the activity of neurons from the globus pallidus of parkinsonian primates during passive limb movements and to determine the extent to which they interact and synchronize. The vast majority (80/103) of the recorded pallidal neurons responded to periodic flexion-extension movements of the elbow. The response pattern was sinusoidal-like and the timing of the peak response of the neurons was uniformly distributed around the movement cycle. The interaction between the neuronal activities was analyzed for 123 simultaneously recorded pairs of neurons. Movement-based signal correlation values were diverse and their mean was not significantly different from zero, demonstrating that the neurons were not activated synchronously in response to movement. Additionally, the difference in the peak responses phase of pairs of neurons was uniformly distributed, showing their independent firing relative to the movement cycle. Our results indicate that despite the widely distributed activity in the globus pallidus of the parkinsonian primate, movement encoding is dispersed and independent rather than correlated and synchronized, thus contradicting current views that posit synchronous activation during Parkinson's disease

Magnetoreception systems in birds: A review of current research

At least two independent systems of magnetoreception are currently believed to exist in birds, based on different biophysical principles, located in different parts of their bodies, and with different neuroanatomical mechanisms. One magnetoreceptory system is located in the retina, and may be based on photochemical reactions on the basis of cryptochrome. Information from these receptors is processed in a specialized part of visual Wulst, the so-called Cluster N. There are good reasons to believe that this visual magnetoreceptor processes compass magnetic information necessary for migratory orientation. The second magnetoreceptory system is probably iron-based (biogenic magnetite), located somewhere in the upper beak (its exact location and ultrastructure of receptors remain unknown) and innervated by the ophthalmic branch of trigeminal nerve. It cannot be ruled out that this system participates in spatial representation and helps forming either a kind of map or more primitive signpost sense (identification of specific geographic regions), based on regular spatial variation of the geomagnetic field. The magnetic map probably enables navigation of migrating birds across hundreds and thousands of kilometres. Apart from these two systems, whose existence has been convincingly shown (even if some details are not fully clear yet), there is evidence for the existence of magnetoreceptors based on the vestibular system. It cannot be ruled out that iron-based magnetoreception takes place in lagena (a part of inner ear in fishes, amphibians, reptiles and birds), and the information perceived is processes in vestibular nuclei. The very existence of this magnetoreception system needs verification, and its function remains completely open