If you think of groups of neurons in arbitrary dimensions, where some groups fire together for some things, and a different group with some overlap fire for oth

If you think of groups of neurons in arbitrary dimensions, where some groups fire together for some things, and a different group with some overlap fire for other things, then it's like two dimensions where a line is a sense or thought and the lines are crossing where they fire for both memories. So two thoughts along two dimensions can cross and light up that subset of neurons. If the two thoughts, or lines, are orthogonal, then not many neurons are both firing for thoughts. If you have many many neurons, and many many memories, then the dimensionality, or possible subsets of firing neurons, is huge. Like our two lines but now in three dimensions, there are a lot of ways for them not to overlap. So the possibility that many things in that space are orthogonal is likely. In a highly dimensional space, a whole lot of things don't overlap.