OSCILLATORY FIRING AND INTERNEURONAL CORRELATIONS IN SQUIRREL-MONKEY STRIATE CORTEX

1. This work explores a mechanism that the brain may use for linking r elated percepts. It has been proposed that temporal relationships in t he firing of neurons may be important in indicating how the stimuli th at activate those neurons are related in the external world. Such temp oral relationships cannot be seen with conventional receptive field ma pping but require cross-correlation and auto-correlation analysis. 2. In the cat and the macaque monkey, cells with similar receptive field properties show correlated firing even when their receptive fields do not overlap. Here I report that in the squirrel monkey, as in the cat, pairs of cells less than or equal to 5 mm apart can show correlated f iring, and these correlations between pairs of cells are often stronge r when they are stimulated by a single contour. This suggests that the correlations reflect not only permanent connections between cells wit h similar receptive fields, but in addition may encode information tha t the activating stimuli are continuous or part of a single object. I also find that, as in the cat, and contrary to some other reports on e xperiments in monkeys, the correlated firing is often rhythmic. These recordings further indicate that peri ods of rhythmicity are associate d with stronger interneuronal syn chrony, which is consistent with the hypothesis that recurrent feedback loops are involved in generating b oth. 3. Pairs of cells in the same cortical column, but at different d epths also showed correlated firing, but with several milliseconds dif ference in timimg between layers. This was true for cells at different depths within layer 2/3 and for pairs of cells in different layers (2 /3 vs. 4B or 4C alpha), providing evidence for cross-talk between the magno- and parvocellular streams.