Types of Spatial Navigation - Essay Example

SPATIAL NAVIGATION INTRODUCTION Spatial navigation is the process of navigating in the environment, over many different scales. Large scale navigation is found among birds, insects, fishes and other animals in migrating over a very long distance. Celestial cues, circadian rhythm and geomagnetism predispose in this type of large scale navigation. Middle scale navigation is an animal’s ability to move around its environment in search of food, mates and sites. Time and space are purely abstract. Like calendars and clocks, objects are the tools with which the abstract entity of space is just measured. The role of the self and the capability of the brain of the perceiver are crucial to the perception of the space. Spatial navigation differs from species to species and among human themselves depending upon the capacity of the brain. During visualisation, the mental representation has a definite spatial extent. (Denis M and Kosslyn K.M, 1999). The area in the brain where visualisation process occurs are well organised so that the images on the retina are laid out on the cortex. This cortical area of the brain is named the topographically organised areas. Researchers have found that these topographically organised areas of the brain are activated even when visualisation is attempted with closed eyes. (Kosslyn S.M et al, 1993). Images of this type alone, in which the surfaces of the objects are clearly depicted, activate the topographically organised areas of the brain. But other types of images such as the sense of things where the objects are around at a given moment do not activate these topographically organised areas in the brain. Such spatial images are found even among the blind. (Mellet E et al, 1998). These sense related spatial images explain the spatial navigational capabilities in animals, birds and insects. Spatial Navigation in birds and insects: Let us first take some case of insects that navigate among themselves and their properties. Researches have shown that the sense oriented navigational capabilities in insects are commonly instinctual. Randolf Menzel et al 2005 have found that honey bees posses a rich map-like organisation of spatial memory in navigating. By recording the flights and dance patterns of the honey bees during forage flights and leaving the feeder and the hive, the team was able to establish that a sequence of behavioural routines were apparent. They extracted two essential criteria of a map-like spatial memory in honey bees. They are: (i) honey bees can set course at any arbitrary location in their familiar area, the familiarity being expressed by the waggle dance pattern (ii) bees can choose between at least two goals. (Randolf Menzel et al, 2005). The use of a cognitive map is well established in birds and insects that are capable of finding a short cut and calculate a novel route from the stored geometrical locations of their nests and food sites.(Neurothology lecture No.8) Uwe Homberg, 2004, found that locust Schistocerca gregaria relied mainly on solar compass and polarisation pattern of the sky for their long-range navigation. He established that the polarisation vision in locusts relied on specialised photoreceptor cells in a small dorsal rim area of their compound eye. Polarised light signalling occurred in the specific area of lamina, medulla and lobula of the optic lobe in the insect’s brain. Integration of polarised-light signals with information on solar positions appeared to start in the optic lube where as the polarisation-opponent interneurons formed a network of inter connected neurons. (Uwe Homberg, 2004). Area of brain involved in spatial navigation: Most studies indicated that hippocampus was the chief area of the brain involved in spatial navigation. Lesion studies have confirmed this and birds with hippocampal lesion, although repeatedly visited their familiar sites made large number of errors. Comparative studies have shown that food storing birds had larger hippocampal area while birds that do not store food do not have. Researches have also pointed out that there existed a sex difference in the size of hippocampus. Female cowbirds that lay eggs on the nests of other birds have larger hippocampus than the male ones. Land mark location: Birds generally rely more on the appearance, size, colour and related properties of the objects near the cache. The actual appearance of the cache is less prioritised by the birds than the location of the cache. This trait in birds were confirmed in experiments in which removal or shifting of larger land marks made notable changes in the behaviour of the birds. (Sherry D.F and S.J.Duff, 1997) SPATIAL NAVIGATION IN HUMAN: Spatial navigation in human also involves neural representation of environment centred spatial locations. Developments in human capacities to measure distances in terms of specified units have both the positive and negative effects in their spatial navigational endeavour. Invention of even the light year in space research does not allow human to observe environmental changes completely. Use of natural geometric cues like sun compass and other environmental objects are ever compared with human calculation of distances and measurement of spatial objects in terms of units invented. One can actually see or perceive an object, say a flower at a distance of 3 feet. If the object is kept farther by a foot at 4 feet from the eyes, can he/she fix the sight at the old site at 3 feet in the empty space? This is the limitation in the spatial extent of human brain. Or this can be construed as the incompetence of human invention of units of distance measurement. Researches have shown that three important variables are involved in human navigation research: 1. The stimuli employed to examine navigation and their manipulation. 2. The sex and age of human subjects and 3. The neural network supporting navigation and possible functions of its key elements. Virtual reality environments were found to stimulate well and characterise the cognitive process engaged in dynamic spatial navigation by human. Studies using computer stimulated environments have found that male advantages in navigation performance using either landmark-free or landmark-limited environments. Age of human subjects too found have the impact on navigation performance. Adult humans were found to take account of non-geometric as well as geometric cues to aid orientation when compared with young children who relied mainly on geometric properties of the environment. Studies comprising imaging of navigation so far have not fit with the hippocampal encoding /retrieval model. However recent rodent studies explored the dorsal/ventral distinction, which is likely to be equivalent to the posterior or interior distinction in humans. (Eleanor A Maguire et al, 1999) As known earlier, hippocampus is still considered to be the chief area of brain involved in spatial navigation. However, functional imaging studies and theoretical models underscore the importance of extra-hippocampal regions as well. Scott D. Moffat et al, 2006 studied healthy adult volunteers, who completed virtual navigation rask and underwent MRI (magnetic resonance imaging) to assess volumes of the caudate neucleus, cerebellum, hippocampus, prefrontal and primary visual cortices. The team was able to conclude that robust age related differences in place learning were evident. They also pointed out that high performance in virtual navigation task was associated with larger volumes of caudate nucleus and prefrontal grey and white matter too. Larger hippocampal volume was associated with improved performance of spatial navigation in younger participants but not in older population. Thus the team was confident enough to ascertain that both hippocampal areas and extra-hippocampal areas of human brain were involved in successful navigational performance. (Scott D. Moffat, et al, 2006) CONCLUSION: To take intelligent decisions on many occasions humans need to integrate prior experiences, current conditions and future expectations comprising a complex process of learning. During such functioning, interactions between multiple brain regions allow an organism to be cognizant of the most effective action to take given the current context. Spatial navigation is an excellent functioning process involving multi regional employment of brain structures. A fundamental problem in neuroscience is to determine how different forms of information pertinent to the production of an organised behaviour be compiled. Brain regions termed ‘associative’, which receive convergent input from many other brain regions, form the centre of the answer to the fundamental problem. Since neurons within the hippocampal region get activated by specific aspects of a route traversal such as spatial location, it is commonly considered that hippocampal area is critical of spatial navigation. However researches have shown that other regions of brain in addition to hippocampus too contribute to the efficient functioning of spatial navigation. For example, prefrontal cortex registers the reason of the series of path-running behaviours. (Scientific Report from Neuroscience Institute, California). Age differences in navigational capacities could be explained with reference to the evolutional learning developments, whereas sex difference could not be explained simply by neuronal studies. Further research in consonance with cultural implications is required to pass light on sex differences in navigational capabilities. Thus spatial navigation in humans too is an unending endeavour of learning process. Space research is naturally an evolutional development in human learning process. Invention of worldly units like meters, kilometres and miles and celestial units like light year are the outcome of human spatial navigational improvements. * * * * * * Reference List— Denis M and Kosslyn K.M, 1999, “Scanning visual images: a window on the mind, Current Psychology of Cognition, 18, 409-465 Eleanor A Maguire, Neil Burgess and John O’Keefe, 1999, “Human spatial navigation:cognitive maps, sexual dimorphism and neural substrates”, Current Opinion in Neurobiology, 9:171-177, Elsevier Science Ltd. Kosslyn S.M, Alpert N.M, Thompson W.L, Maljkovic V, Weise S.B, Chabris C.F, Hamilton S.E, and Buonano F.S, 1993, “Visual mental imagery activates topographically organised visual cortex: PETinvestigations, Journal of Cognitive neuroscience, 5, 263-287 Mellet E, Petit L, Mazoyer B, Denis M and Tzourio N, 1998, “Reopening the mental imagery debate:lessons from the functional neuro anatomy, NeuroImage, 8, 129-139 Neurothology lecture No.8 dated 24.02.1998 on Spatial navigation and cognitive maps retrieved from http://www.nervana.montana.edu/courses/bio480/netholec8.html on 23.5.2007 Randolf Menzel, Uwe Greggers, Alan Smith, Sandra Berger, Robert Brandt, Sascha Brunke, Gesine Bundrock, Sandra Hulse, Tobias Plumpe, Frank Schaupp, Elke Schuttler, Silke Stach, Jan Stindt, Nicola Stollholf and Sebastien Watzl, 2005, “honey bees navigate according to a map-like spatial memory”, Neuroscience, Vol. 102, No.8: 3040-3045 Scientific Report from Neuroscience Institute, California, dated December 2005, pp18-19 Scott D. Moffat, Kristen M.Kennedy, Karen M. Rodrigue and Naftali Raz, 2006, “Extrahippocampal Contributions to Age differences in Human Spatial Navigation”, Cerebral Cortex Advance access, doi:10.1093/cercor/bhl036 published on line on July 20, 2006 @ http://cercor.oxfordjournals.org/papbyrecent.dtl Sherry D.F and S.J.Duff, 1997, “Behavioural and Neural Basis of Orientation in Food Storing Birds, JEB, 199:165-172 Uwe Homberg, 2004, “In search of the sky compass in the insect brain”, Naturwissenschaften, Vol 91, No. 5: 199-208, Springer, Berlin Read More