User:ProtoplasmicKisses1/sandbox

Overview
The H1 Neuron is located in the visual cortex of flies such as Diptera, and mediates motor responses to visual stimuli. H1 (Horizontal 1) is sensitive to motion in the visual field and enables the fly to rapidly and accurately respond to optic flow with motor corrections to stabilize flight. H1 is particularly responsive to horizontal forward motion associated with movement of the fly’s own body during flight. Damage to H1 impairs the fly’s ability to counteract disturbances during flight, suggesting that it is a necessary component of the optomotor response. H1 is an ideal system for studying the neural basis of information processing due to its highly selective and predictable responses to stimuli. Since the initial anatomical and physiological characterizations of H1 in 1976, study of the neuron has greatly benefited the understanding of neural coding in a wide range of organisms, especially the relationship between the neural code and behavior.

Anatomy
Flies possess two H1 neurons, one in each hemisphere of the brain. H1 is located in the lobula plate of the optic lobe, the final destination of visual information originating from photoreceptors of the eye. The lobula plate forms the posterior part of the lobula complex where the lobula plate tangential cells (LPTCs) are located. The large process diameter of these neurons allowed them to be amongst the first visual neurons to be intracellularly recorded in the fly. .

Connectivity
Fly eyes are comprised of many individual ommatidia that posses their own lenses and photoreceptors. The dendritic arbor of the H1 neuron covers the anterior surface of the lobula plate, where it receives retinotopic input from interneurons of the medulla lobula. H1 has dendro-dendritic synapses with centrifugal horizontal (CH) cells that descend to the flight motor. To respond to image motion it the H1 neuron sends action potentials of varying frequency to the contralateral lobula plate. .

Hardwiring
Unlike human brains that rely on experience-dependent neuronal plasticity, the brain of the fly is hardwired for particular tasks in the visual sensory system. The H1 neuron and related tangential neurons are suggested to be genetically determined, meaning that these neurons are unaffected by visual stimuli during early development. Parts of the fly brain have neuroplasticity but the H1 and other tangential neurons are hardwired neuronal machinery. Genetic hardwiring is likely an adaptation strategy that allow the flies to navigate in flight soon after hatching, actions largely mediated by the H1 and related tangential neurons.

Role Within Diptera
Flies are agile flyers and strongly depend on vision during flight. For visual course control, flies optic flow field is analyzed by a set of ∼60 motion-sensitive neurons, each present in the third visual neuropil of the left and right eyes. A subset of these neurons is thought to be involved in using the optic flow to estimate the parameters of self-motion, such as yaw, roll, and sideward translation. Other neurons are thought to be involved in analyzing the content of the visual scene itself, for example, to separate figure from ground using motion parallax. The H1 neuron is responsible for detecting horizontal motion across the entire visual field of the fly, allowing the fly to generate and guide stabilizing motor corrections mid-flight with respect to yaw.

Exploring the Neural Code
Two characteristics of H1, reliability and specificity, make it exceptionally well suited for testing proposed models of neural encoding.

Reliability
H1 is a very efficient encoder of information and is highly resilient to stimulus noise from external sources. The operational and encoding processes of sensory pathways are often negatively affected by both external noise (relating to the stimulus) and internal noise (imperfect physiological processes); however, the activity of H1 is unaffected by photon noise. Instead, noise intrinsic to the H1 neural architecture is the limiting factor for accurate responses to stimuli. This dramatically reduces the noise of H1 electrophysiological readings, and provides the reliability necessary for accurate study conclusions.

Specificity
H1 exhibits very specific and predictable responses to stimuli, characteristics that are greatly beneficial for exploring the neural code because they allow for confident correlations between neural activity and stimuli. In particular, H1 exhibits a response to the stimulation of a single ommatidium, and can discriminate between translational motion of 2-3˚ in the visual field