setwd("~/data/observation1")

library(ggplot2)
ggplot(a, aes(x = place, y = firing_rate)) + geom_point() + geom_path()

files <- list.files(pattern=".txt")
for (i in files){
  mylist <- lapply(setNames(files, files), read.table, header = T)
  mylist <- lapply(names(mylist), function(i) {cbind(mylist[[i]], ID = i)})
  mydata <- do.call(rbind, mylist)
}

ggplot(mydata, aes(x = place, y = firing_rate, colour = ID)) + geom_point() + geom_path()
dev.print(pdf, 'observation1.pdf')