Abstract
We describe the first underwater electroencephalography (EEG) involving octopuses. We can detect stimulus frequency-dependent correlates of flickering LEDs in electrodes placed on their skin under saltwater. This activity is biological in origin, because control experiments rule out that this activity is generated by the flickering light alone in the absence of an octopus. Rather than place electrodes onto the skin of an octopus, we place the octopus between two layers of fixed electrodes under saltwater, while presenting the octopus with visual input from outside its enclosure. We flickered light at various fixed frequencies outside of a transparent enclosure that held individual octopus bimaculoides, loosely sandwiched between two plates containing embedded EEG tripolar electrodes. Neural activity entrained to displayed frequencies can be detected as potential from electrodes situated on or near the midpoint between the two eyes of the octopus, but not from electrodes situated below the brain of the octopus. We are able to detect SSVEPs at multiple tested frequencies. EEG offers the major advantage that it is not invasive, so octopuses need not be fixed in place or anaesthetized. The parallel alignment of neurons in their brain’s vertical lobe allows summation of the Local Field Potential (LFP) that emerges from MSF/MIF axons synapsing on the AM cells of the vertical lobe. There is also a similar co-alignment of neurons in some of the other octopus brain lobes, which may permit LFP summation of signals. Conclusion: An electrode placed near the center of the two eyes is able to detect neural responses to light flickering at various frequencies. Octopus EEG may eventually prove to be as fruitful as human EEG has proven to be in deciphering the neural correlates of complex cognition.