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. 2011 Oct 28;5:69. doi: 10.3389/fnbeh.2011.00069

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Copyright © 2011 Deshmukh and Knierim.

This is an open-access article subject to a non-exclusive license between the authors and Frontiers Media SA, which permits use, distribution and reproduction in other forums, provided the original authors and source are credited and other Frontiers conditions are complied with.

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Figure A1 — Spatial information in LEC is higher in an open field containing objects compared to an empty field. To test whether the higher spatial information recorded with objects in the present study, compared to previous studies (Hargreaves et al., 2005; Yoganarasimha et al., 2010), was an artifact of uncontrolled differences between the studies, 25 LEC units in two rats were recorded in sessions with (session 1) and without (session 7) objects. Because the LEC firing patterns might have been affected by a prior history of the presence of objects, the session without objects was conducted in a similar box in a different room to minimize such a confound. (A) Firing rate maps of the neurons with higher spatial information scores in the presence of objects than in the absence of objects, sorted in decreasing order of the difference. Note that a number of cells (units 1, 3, 4, 5, 7, and 8) had highly localized, high-rate firing fields in the presence of objects but weaker, more diffuse firing in the absence of objects. Two cells (units 2 and 6) fired at higher rates in the session without objects, but they fired along multiple walls, not in restricted locations. Similar activity along walls has been shown previously (Hargreaves et al., 2005). Peak firing rate (pk, Hz), spatial information score (i, bits/spike) and probability of getting the information score by chance (p) are shown at the top of each plot. Unlike the firing rate maps shown elsewhere in the paper, which were autoscaled between 0 Hz and maximum firing rates within the individual rate maps, the firing rate maps in (A,B) were scaled such that blue corresponds to 0 Hz while red corresponds to the larger of the peak firing rates in the with- and without-object sessions for the given neuron. This cross-session scaling makes it easy to see rate remapping as well as the locations of firing fields. Note that in some cases, the scaling masks low-rate firing that still results in moderate spatial information scores (e.g., units 1 and 4 without objects show information scores of 0.56 and 0.49, respectively, although the peak firing rates and information scores are less than they are with objects). (B) Firing rate maps of the neurons with lower spatial information scores in the presence of objects than in the absence of objects, sorted in decreasing order of the difference. Note the lack of a pronounced difference in spatial firing selectivity between the with-object and without-object sessions in these cells, in contrast with the numerous examples in (A). This contrast argues strongly against a generalized “remapping” interpretation of these data, as such an explanation would predict the number of cells having higher spatial information in the with-objects session to be approximately equal to the number of cells having higher information score in the without-objects environments. On average, the firing rate maps without objects in (A,B) resemble those shown in prior reports of LEC non-spatial firing (Hargreaves et al., 2005; Yoganarasimha et al., 2010), with none of the cells showing robust, highly localized firing, indicating that the increased responsiveness when objects are present is not due to a generalized increase in spatial selectivity in the present study. Both rats included in this analysis were trained extensively in the environment with objects, and the last 2–3 days of training included one foraging session in the environment without objects. The experiments were run over multiple days, making the second room more familiar over time. Furthermore, because the prior studies recorded from highly familiar environments and showed poor spatial selectivity in LEC, the similar lack of spatial selectivity without objects in the present study is unlikely a result of the relative novelty of the environment without objects. (C) Comparison of spatial information scores of LEC neurons in the presence and absence of objects. Red lines connect spatial information scores in the presence (+) and in the absence (−) of objects for neurons that showed higher spatial information scores in the presence of objects than in the absence of objects, shown in (A). Blue lines connect spatial information scores for neurons that showed lower spatial information in the presence of objects than in the absence of objects, shown in (B). Visually, the slopes of the red lines are on average greater than the slopes of the blue lines, indicating that a number of cells that had high spatial information in the presence of objects lost this tuning in the absence of objects. There were no neurons that had high spatial information in the absence of objects and much lower information in the presence of objects (i.e., there are no blue lines with a steep slope), arguing against a general remapping explanation for differences between the environments. Across all neurons, the spatial information scores were significantly higher in the presence of objects than in the absence of objects (with-objects median = 0.33 bits/spike, without-objects median = 0.24 bits/spike; Wilcoxon signed rank test, p = 0.04).This difference was even more significant when only the 23 cells with significant information scores (p < 0.01) in at least one of the two sessions were included (with-objects median = 0.33 bits/spike, without-objects median = 0.22 bits/spike; Wilcoxon signed rank test, p = 0.017).

Figure A1 — Spatial information in LEC is higher in an open field containing objects compared to an empty field. To test whether the higher spatial information recorded with objects in the present study, compared to previous studies (Hargreaves et al., 2005; Yoganarasimha et al., 2010), was an artifact of uncontrolled differences between the studies, 25 LEC units in two rats were recorded in sessions with (session 1) and without (session 7) objects. Because the LEC firing patterns might have been affected by a prior history of the presence of objects, the session without objects was conducted in a similar box in a different room to minimize such a confound. (A) Firing rate maps of the neurons with higher spatial information scores in the presence of objects than in the absence of objects, sorted in decreasing order of the difference. Note that a number of cells (units 1, 3, 4, 5, 7, and 8) had highly localized, high-rate firing fields in the presence of objects but weaker, more diffuse firing in the absence of objects. Two cells (units 2 and 6) fired at higher rates in the session without objects, but they fired along multiple walls, not in restricted locations. Similar activity along walls has been shown previously (Hargreaves et al., 2005). Peak firing rate (pk, Hz), spatial information score (i, bits/spike) and probability of getting the information score by chance (p) are shown at the top of each plot. Unlike the firing rate maps shown elsewhere in the paper, which were autoscaled between 0 Hz and maximum firing rates within the individual rate maps, the firing rate maps in (A,B) were scaled such that blue corresponds to 0 Hz while red corresponds to the larger of the peak firing rates in the with- and without-object sessions for the given neuron. This cross-session scaling makes it easy to see rate remapping as well as the locations of firing fields. Note that in some cases, the scaling masks low-rate firing that still results in moderate spatial information scores (e.g., units 1 and 4 without objects show information scores of 0.56 and 0.49, respectively, although the peak firing rates and information scores are less than they are with objects). (B) Firing rate maps of the neurons with lower spatial information scores in the presence of objects than in the absence of objects, sorted in decreasing order of the difference. Note the lack of a pronounced difference in spatial firing selectivity between the with-object and without-object sessions in these cells, in contrast with the numerous examples in (A). This contrast argues strongly against a generalized “remapping” interpretation of these data, as such an explanation would predict the number of cells having higher spatial information in the with-objects session to be approximately equal to the number of cells having higher information score in the without-objects environments. On average, the firing rate maps without objects in (A,B) resemble those shown in prior reports of LEC non-spatial firing (Hargreaves et al., 2005; Yoganarasimha et al., 2010), with none of the cells showing robust, highly localized firing, indicating that the increased responsiveness when objects are present is not due to a generalized increase in spatial selectivity in the present study. Both rats included in this analysis were trained extensively in the environment with objects, and the last 2–3 days of training included one foraging session in the environment without objects. The experiments were run over multiple days, making the second room more familiar over time. Furthermore, because the prior studies recorded from highly familiar environments and showed poor spatial selectivity in LEC, the similar lack of spatial selectivity without objects in the present study is unlikely a result of the relative novelty of the environment without objects. (C) Comparison of spatial information scores of LEC neurons in the presence and absence of objects. Red lines connect spatial information scores in the presence (+) and in the absence (−) of objects for neurons that showed higher spatial information scores in the presence of objects than in the absence of objects, shown in (A). Blue lines connect spatial information scores for neurons that showed lower spatial information in the presence of objects than in the absence of objects, shown in (B). Visually, the slopes of the red lines are on average greater than the slopes of the blue lines, indicating that a number of cells that had high spatial information in the presence of objects lost this tuning in the absence of objects. There were no neurons that had high spatial information in the absence of objects and much lower information in the presence of objects (i.e., there are no blue lines with a steep slope), arguing against a general remapping explanation for differences between the environments. Across all neurons, the spatial information scores were significantly higher in the presence of objects than in the absence of objects (with-objects median = 0.33 bits/spike, without-objects median = 0.24 bits/spike; Wilcoxon signed rank test, p = 0.04).This difference was even more significant when only the 23 cells with significant information scores (p < 0.01) in at least one of the two sessions were included (with-objects median = 0.33 bits/spike, without-objects median = 0.22 bits/spike; Wilcoxon signed rank test, p = 0.017).