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Overview[edit]

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.[1] H1 is particularly responsive to horizontal forward motion associated with movement of the fly’s own body during flight.[2] 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.[3] 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[edit]

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.[4] 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. [5].

Connectivity[edit]

Fly eyes are comprised of many individual ommatidia that posses their own lenses and photoreceptors.[6] 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.[7] To respond to image motion it the H1 neuron sends action potentials of varying frequency to the contralateral lobula plate.[8].

Hardwiring[edit]

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.[9] 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.[10]


Role Within Diptera[edit]

Flies are agile flyers and strongly depend on vision during flight.[11] 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.[12] 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.[13] 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.[14][15] 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.[16]

Exploring the Neural Code[edit]

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

Reliability[edit]

H1 is a very efficient encoder of information and is highly resilient to stimulus noise from external sources.[17] 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[edit]

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[18]

References[edit]

  1. ^ Frye M., Dickinson M. Fly Flight: A Model for the Neural Control of Complex Behavior, Neuron, Volume 32, Issue 3, 8 November 2001, Pages 385-388, ISSN 0896-6273, 10.1016/S0896-6273(01)00490-1. (http://www.sciencedirect.com/science/article/pii/S0896627301004901)
  2. ^ Eckhert, Hendrik. Functional properties of the H1-neurone in the third optic ganglion of the blowfly, Phaenicia. J Comparative Physiology, Volume 135, Issue 1, 1980. Pages 29-39. http://link.springer.com/article/10.1007%2FBF00660179#
  3. ^ Neri, Peter. Spatial integration of optic flow signals in fly motion-sensitive neurons. Journal of Neurophysiology. Volume 95, no. 3, March 2006, pages 1608-1619. http://www.ncbi.nlm.nih.gov/pubmed/16338996
  4. ^ Hausen, K. Functional characterization and anatomical identification of motion sensitive neurons in the lobula plate of the blowfly Calliphora erythrocephala. Z. Naturforsch. 31c, 629-633, 30 June, 1976.
  5. ^ Borst, A., Haag, J. Neural networks in the cockpit of the fly. Journal of Comparative Physiology. July 2002; 188(6):419-37. http://www.ncbi.nlm.nih.gov/pubmed/12122462
  6. ^ Borst, A., Haag, J. Neural networks in the cockpit of the fly. Journal of Comparative Physiology. July 2002; 188(6):419-37. http://www.ncbi.nlm.nih.gov/pubmed/12122462
  7. ^ Juergen, H., Borst, A. Dendro-dendritic interactions between motion-sensitive large-field neurons in the fly. The Journal of Neuroscience. 15 April 2002, 22(8): 3227-3233
  8. ^ Borst, A., Haag, J. Neural networks in the cockpit of the fly. Journal of Comparative Physiology. July 2002; 188(6):419-37. http://www.ncbi.nlm.nih.gov/pubmed/12122462
  9. ^ Karmeier K., Tabor R., Egelhaaf M., Krapp HG. Early visual experience and the receptive-field organization of optic flow processing interneurons in the fly motion pathway. Journal of Visual Neuroscience. Volume 18, no. 1, Jan-Feb 2001, pp 1-8. http://www.ncbi.nlm.nih.gov/pubmed/11347806
  10. ^ Karmeier K., Tabor R., Egelhaaf M., Krapp HG. Early visual experience and the receptive-field organization of optic flow processing interneurons in the fly motion pathway. Journal of Visual Neuroscience. Volume 18, no. 1, Jan-Feb 2001, pp 1-8. http://www.ncbi.nlm.nih.gov/pubmed/11347806
  11. ^ Martin Egelhaaf, Roland Kern. Vision in flying insects. Current Opinion in Neurobiology, Volume 12, Issue 6, 1 December 2002, Pages 699–706. http://dx.doi.org/10.1016/S0959-4388(02)00390-2
  12. ^ Haag J., Borst A. Dendro-Dendritic Interactions between Motion-Sensitive Large-Field Neurons in the Fly. The Journal of Neuroscience. April 15, 2002. 22(8):3227-3233. http://www.jneurosci.org/content/22/8/3227.full.pdf
  13. ^ Hausen K, Egelhaaf M (1989) Neural mechanisms of visual course control in insects. In: Facets of vision (Stavenga DG, Hardie RC, eds), pp 391-424. Berlin: Springer.
  14. ^ Egelhaaf M (1985) On the neuronal basis of figure-ground discrimination by relative motion in the visual-system of the fly. 2. Figure-detection cells, a new class of visual interneurones. Biol Cybern 52: 195-209.
  15. ^ Kimmerle B, Egelhaaf M (2000) Performance of fly visual interneurons during object fixation. J Neurosci 20: 6256-6266.
  16. ^ Eckert H (1980) Functional properties of the H1-neurone in the third optic ganglion of the blowfly, Phaenicia. Journal of Comparative Physiology A: Neuroethology
  17. ^ Grewe, J., Kretzberg, J., Warzecha, A. Impact of photon noise on the reliability of a motion-sensitive neuron in the fly’s visual system. The Journal of Neuroscience. 26 Novermber, 2003. 23(34):10776-10783 http://www.jneurosci.org/content/23/34/10776.full.pdf
  18. ^ Borst, A., Haag, J. Neural networks in the cockpit of the fly. Journal of Comparative Physiology. July 2002; 188(6):419-37. http://www.ncbi.nlm.nih.gov/pubmed/12122462

Further Reading[edit]

  • Quiroga RQ, Nadasdy Z, Ben-Shaul Y (2004) Unsupervised spike detection and sorting with wavelets and superparamagnetic clustering. Neural Comput 16:1661–1687
  • Reiser MB, Dickinson MH (2008) A modular display system for insect behavioral neuroscience. Journal of Neuroscience Methods 167:127–139
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