Department of H&SS, Indian Institute of Technology Guwahati, India Sleep and Navigation: Does Sleep Differentially Modulate Cognitive Strategies of Navigation?   Naveen Kashyap, PhD Department of H&SS, Indian Institute of Technology Guwahati, India Introduction Cognitive Strategies of Navigation   Navigation has been essential part of human survival. Navigation across large environments like cities, require humans to form mental representations of the environments. This helps them in following familiar routes and perhaps to plan new routes. These mental representations have been the subject of numerous studies in human spatial cognition and development. Different strategies can be used to navigate in the environment (Berthoz, 2001). To reach a target location one can use the cognitive map of the environment (spatial memory) by thinking about the landmarks and their spatial relationships (O’Keefe & Nadel, 1978). Alternatively, one can use distance from a single landmark as a reference or make choices with respect to body motion, independent of the landmarks available in the environment. The present study employ the above mentioned cognitive strategies for navigation in virtual complex environments. Sleep and Navigation Experimental evidences from recent studies conclude the positive role of sleep in consolidation of recent memories (Maquet et.al. 2003). Processes during sleep actively alters, restructure and strengthen information acquired during wakefulness. The robust memory trace as a result of these processes lead to long-term adaptation of the behavioral responses to the environment (McGaugh, 1966). Several studies on rodents suggest, firing patterns observed in hippocampal neuronal ensembles during spatial behavior being reactivated during NREM sleep. This offline replay of hippocampal activity during NREM sleep in rodents is involved in the consolidation of newly encoded spatial information (Quin et.al., 1999, Sutherland & McNaughton, 2000). In humans spatial memory acquisition involves the hippocampus and other medial temporal lobe regions similar to rodents (Burgess et.al., 2002). Recent position emission tomographic (PET) / functional magnetic resonance imaging (fMRI) studies of spatial/topographic memory have repeatedly described learning related changes in the hippocampal formation and in the parahippocampal gyrus during human navigation in virtual environments. More recently Peigneux et.al, 2004 have found that in humans the amount of hippocampal activity expressed during slow wave sleep positively correlates with the improvement of performance in virtual navigation on the next day. Stimuli & Task Virtual Environment: Computer simulation game. The game employed the two cognitive strategies of navigation Map (spatial) & No-Map (non-spatial). The participants were divided into two groups (spatial vs non-spatial). Each participant within a group contributed to both the sleep and sleep deprived night. Polysomnography: 10 channel EEG with 10-20 montage was recorded using disc electrodes and analyzed for sleep parameters using AASM Criteria Procedure At the beginning each participant was explained about the study and was allowed to interact with the computer game till he felt comfortable to play the game. The procedure for the study is explained in the table below Statistics   Reaction times while performing both test and retest sequences were used for statistical analysis. The data obtained was submitted to 2x2x2 factorial ANOVA with repeated measure on groups (sleep, sleep deprivation) x session (test, retest) as within subject factor and strategy (spatial, non – spatial) as between subject factor. Speed Measure The repeated measure ANOVA with reaction times as dependent measure showed a significant main effect of session (F1,8 = 10.113; p = 0.013): the two groups increased their speed while performing the retest session and group x session interaction (F1,8 = 140.64, p = 0.001). The main effect of group (F1,8 = 3.663; p = 0.092), strategy (F1,9 = 0.13; p = 0.75) and all other interactions were not significant. Sleep Navi Task Night 1 (test) Sleep / Awake Day 1 Recall   Day 2 Night 2 (test) Group 1 (map) 1) Report: 9 pm 2) Practice Task: 3x10 = 30 min 3) Main Task: 1x30 = 30 min 4) Sleep / Awake 10 pm – 6 am Subjects are required to perform on the task at 07:00 hrs after 8 hrs of either sleep / awake Group 2 (Non- map) Fig 2: Mean reaction times of the experimental groups at the test and retest sessions Conclusions In the present study we investigated the effects of sleep on different cognitive strategies of navigation. The two strategy we tested were spatial (map-based) and non-spatial (non-map based). The following conclusion can be drawn Both the accuracy and speed measure suggest that sleep does not significantly modulate cognitive strategies differentially Spatial learning independent of the cognitive strategy is however benefited for the sleep group as compared to the wake (sleep deprivation) group. Accuracy (Mean number of errors decrease) improved Reaction times (Speed measure increase) decreased across sleep group on test-retest sessions Stage 2 (N2) sleep highly correlated to performance benefit in the sleep group over test-retest session (ῤ = 0.61). Results Analysis Accuracy Measure The factorial ANOVA for mean errors made in the test and retest session showed a significant main effect session (F1,8 = 17.067, p = 0.003), group x session interaction (F1,8 = 22.56, p = 0.001). The main effect of group (F1,8 = 0.12, p = 0.91), strategy (F1,9 = 0.05, p = 0.9) and other interactions were not significant. The sleep group showed a test-retest decrease in number of errors (mean decrease = -2.7). The sleep deprived group showed a increase of errors in the test-retest session (mean increase = 1.1) The Present Proposal   Two major conclusions that appear from the above cited literature are – Human employ different cognitive strategies for navigating complex environments and – Sleep plays positive role in the consolidation of hippocampal and medial temporal lobe dependent spatial memory. In the present proposal we posit to test the hypothesis whether sleep differentially benefits the two types of cognitive strategies mentioned in the literature above References 1) Berthoz, A., (2001) Neural basis of spatial orientation and memory of routes: Topokinetic memory or Topokinesthesic memory , Rev Neurol, 779-789 2) Maquet, P., Smith, C., & Stickgold, R., (2003) Sleep and brain plasticity (Oxford: Oxford University Press) 3) O’Keffe, J ., & Nadel, L., (1978) The hippocampus as a cognitive map. Oxford: Clarendon 4) Peigneux, P, et.al. (2004) Are spatial memories strengthen in the human hippocampus during slow wave sleep? Neuron, 535-545 Materials and Methods Participants: Ten healthy paid participant (mean age: 22.5 yrs., all males) participated in the study. None of the subjects had history of medical, neurological or psychiatric disorders. Informed consent was obtained from all participants and the study was approved by local ethics committee. Participant served as their own control by participating on both the sleep & sleep – deprived nights. Acknowledgements The Present work was funded by Department of Science and Technology, India via project no SR/FT/LS-172/2008. Fig 1: Average Errors (of the experimental groups) while performing test –retest sessions