Changes in the Inferior Colliculus Associated with Hearing Loss: Noise-Induced Hearing Loss, Age-Related Hearing Loss, Tinnitus and Hyperacusis
Alan R. Palmer and Joel I. Berger
The inferior colliculus is an important auditory relay center that undergoes fundamental changes following hearing loss, whether noise induced (NIHL) or age related (ARHL). These changes may contribute to the induction or maintenance of phenomena such as tinnitus (phantom auditory sensations) and hyperacusis (increased sensitivity to sound). Here, we outline changes that can occur in the inferior colliculus following damage to the periphery and/or as a result of the ageing process, both immediate and long-term, and attempt to disentangle which changes relate to either tinnitus or hyperacusis, as opposed to solely hearing loss. Understanding these changes is ultimately important to reversing the underlying pathology and treating these conditions.
Roy E. Ritzmann and Sasha N. Zill
This article discusses legged locomotion in insects. It describes the basic patterns of coordinated movement both within each leg and among the various legs. The nervous system controls these actions through groups of joint pattern generators coupled through interneurons and interjoint reflexes in a range of insect species. These local control systems within the thoracic ganglia rely on leg proprioceptors that monitor joint movement and cuticular strain interacting with central pattern generation interneurons. The local control systems can change quantitatively and qualitatively as needed to generate turns or more forceful movements. In dealing with substantial obstacles or changes in navigational movements, more profound changes are required. These rely on sensory information processed in the brain that projects to the multimodal sensorimotor neuropils collectively referred to as the central complex. The central complex affects descending commands that alter local control circuits to accomplish appropriate redirected movements.
Leonard K. Kaczmarek
All neurons express a subset of over seventy genes encoding potassium channel subunits. These channels have been studied in auditory neurons, particularly in the medial nucleus of the trapezoid body. The amplitude and kinetics of various channels in these neurons can be modified by the auditory environment. It has been suggested that such modulation is an adaptation of neuronal firing patterns to specific patterns of auditory inputs. Alternatively, such modulation may allow a group of neurons, all expressing the same set of channels, to represent a variety of responses to the same pattern of incoming stimuli. Such diversity would ensure that a small number of genetically identical neurons could capture and encode many aspects of complex sound, including rapid changes in timing and amplitude. This review covers the modulation of ion channels in the medial nucleus of the trapezoid body and how it may maximize the extraction of auditory information.
Alex S. Mauss and Alexander Borst
Visual perception seems effortless to us, yet it is the product of elaborate signal processing in intricate brain circuits. Apart from vertebrates, arthropods represent another major animal group with sophisticated visual systems in which the underlying mechanisms can be studied. Arthropods feature identified neurons and other experimental advantages, facilitating an understanding of circuit function at the level of individual neurons and their synaptic interactions. Here, focusing on insect and crustacean species, we summarize and connect our current knowledge in four related areas of research: (1) elementary motion detection in early visual processing; (2) the detection of higher level visual features such as optic flow fields, small target motion and object distance; (3) the integration of such signals with other sensory modalities; and (4) state-dependent visual motion processing.
Guy Levy, Nir Nesher, Letizia Zullo, and Binyamin Hochner
Motor Control is essentially the computations required for producing coordinated sequences of commands from the controlling system (i.e., nervous system) to the actuation system (i.e., muscles) to generate efficient motion. The level of motor control complexity depends on the number of free parameters (degrees of freedom) that have to be coordinated. This number is much smaller in skeletal animals because they have a rather limited number of joints. In soft bodied animals, like the octopus, this number is virtually infinite. Here we show that the efficient motor control system of the octopus uses solutions that are very different from those of articulated animals, and it involves embodied co-evolution of the unique morphology together with the organization of the nervous and muscular systems to enable control strategies that are best suited for a highly active soft-bodied animal like the octopus.