Across shape peak distance differences
) Within shape rate differences 's Across shape rate differences
8 c Q) 80 I C s E Ç ' Ic Q. m Q r = 0.70, p<0.0001 20
D BP A cr o ss m ean d ifferen ce (P ixels)
r = 0.76, p<0.0001
g UJ
RATE A cr o ss m ea n d ifferen ce (Hz)
C) Rate Within/Across ratio
Vs Peak Distance Within/Across ratio .2
(/) (A O *0 HI a: No significant correlation (p>0.61) * * * * * * * ->* * * * * # * * * * * * * * * * * * * * * * *
DBP W itfiin/A cross ratio
Figure 8e. Scatter plots depicting relationships between variables within and across shapes for 46 place cells o f Experiment 1 A. One cell which does not have a within-shape distance- between-peaks data point is excluded from the scatter plots of A) and C). Note that the axes in the first two graphs are not equal.
and was also excluded from the Across-Shape DBP descriptive statistics. It is included in the CPCP distance index.
The mean W ithin Shape DBP was 29.1 pixels (3.0 pixels sem). The mean Across Shape DBP was 29.4 pixels (2.3 pixels sem). The values are clearly very similar. The linear correlation for the two variables (see scatter plot A in Figure 8e) was r = 0.70, p<0.0001. This suggests that cells with large within-shape DBPs also had large across-shape DBPs, and so on. Such a pattern might well be expected from cells with large fields, or cells that have generally lower reproducibility o f firing. A pairwise t test was performed on these two DBP variables on a cell by cell basis, revealing no significant difference (p>0.89). The mean Within/Across (W/A) DBP ratio for the cells was 1.02 (0.06 sem). (Note that the W/A DBP ratio cannot simply be obtained by dividing the mean within shape DBP by the mean across shape DBP.)
The CPCP distance mean (based on all 46 cells) was 21 pixels. From the Monte Carlo simulation cumulative frequency chart (not shown), the probability o f a single c e ll’s peaks being this close to each other is 0.042, assuming random firing. Since there are
46 cells, it is unnecessary to work out in detail, whether applying the central limit theorem or using the cumulative frequency table since the distribution is somewhat skewed, the vanishingly small probability that the sampled population is composed o f cells with peaks that are not systematically related to each other. Using the 23 pixel cut o ff distance, 30 out o f 46 cells (65%) may be described as homo topic. Table 8.2 gives the percentage o f homotopic cells for other cut off points. The less stringent cutoff o f 25 pixels (the cutoff distance in a 200x200 grid: 2"^ Monte Carlo simulation for experiment 2) produces a figure o f 70% homotopic cells.
The mean within shape rate difference was 2.02 Hz (0.25 Hz sem). The mean across shape rate difference was 2.19 Hz (0.23 sem). The values are again similar. The linear correlation for these two variables (see scatterplot B in Figure 8e) was r = 0.76, p<0.0001. This suggests that cells with relatively high rate differences across shapes showed this pattern simply because they were more variable generally. The pairwise cell-by-cell t test showed no significant differences (p>0.32). The mean cell W/A rate ratio was 0.95 (sem 0.06), again close to unity.
Finally, a scatter plot was made o f the w/a rate ratio for each cell against the w/a DBP ratio for each cell, for 45 cells (see Plot C in Figure 8e). There is no significant correlation (p>0.61). This suggests that there is no tendency for cells which are similar in terms o f peak rate to be similar in terms o f peak position, and so on.
Experiment IB - Day 1 - Quantitative Results - See Table 8.3 and Figure 8f All 20 cells contributed to all measures.
The mean Within Shape DBP was 18.2 pixels (3.0 pixels sem). The mean Across Shape DBP was 21.8 pixels (2.5 pixels sem). The values are clearly very similar. It is notable that they are both smaller than the equivalent values in experiment 1 A. The linear correlation for the two variables (see scatter plot A in Figure 8f) was r = 0.74, p<0.00025. Again, this suggests that cells with large within-shape DBPs also had large across-shape DBPs, and so on. The pairwise t test for these variables revealed no significant difference (p>0.09), though this probability is appreciably smaller than the equivalent statistic in experiment 1 A. The mean Within/Across (W/A) DBP ratio for
VARIABLES
DESCRIPTIVES CORRELATION PAIRWISE t TEST
A) Field Peak Dosition differences W ithin shape DBP (n = 20),
& Across shape DBP (n = 20) Within shape DBP: Mean = 1 8 .2 pixels, sem = 3.0 pixels. A cro ss shape DBP: Mean = 21.8 pixels, sem = 2.5 pixels r= 0.74, F ( l , 18) = 21.76, p<0.00025 d f= 19, t = 1.745, p>0.09 B) Rate differences W ithin shape rate difference (n = 20) & Across shape rate difference (n = 20)
Within shape rate diff: Mean = 1.97 Hz, sem = 0.30 Hz A cross shape: Mean = 2.14 Hz, sem = 0.30 Hz r= 0.88, F ( l , 18) = 59.37, p<0.0001 d f= 19, t = 1.073, p>0.29 C) Within/Across (W/A) ratios Rate W/A ratio (n= 20)
& DBP W/A ratio (n = 20)
Rate w/a ratio: cell mean = 0.96, sem = 0.06 DBP w/a ratio: cell mean = 0.81 sem = 0.07 No significant correlation, p>0.73
D) CPCP measure & Homotopic cells Assuming 23 pixel
cut o ff distance: 18/20 cells are homotopic (90%) The same figures apply to cut off distances o f 21, 25, and 27 pixels.
CPCP distance: mean = 14 pixels sem = 2.0 pixels
Table 8.3 Statistical results table, presenting various statistics associated with a lack o f “remapping” in the animals o f experiment IB. All tests are two-tailed. “Sem” = Standard Error o f the mean. “DBP” is an abbreviation for Distance-between-Peaks.