It is already accepted, that plants possess a specific type of “intelligence”. But do they have an equivalence of a nervous system that would enable them to react like having their own consciousness? For somebody, who is looking for a deeper connection to Nature, as well as for fans of the unorthodox, the topic of plant consciousness is quite an attractive domain.
Some claims assert, that plants can interact with humans in yet unrecognized ways. One of the main sources of this mystery is the research of Cleve Backster from the 1960s [1]. In his book about communication with plants [2], evidence from his measurements is offered, stating that plants feel pain and have extrasensory perception. These opinions were later spread all over the world, perhaps also thanks to his reputation, as Backster was a prominent expert and founder of CIA’s polygraph unit serving for detecting lies based on measurement and analysis of physiological signals.
Back in 2011, we performed our own experiments. For measuring signals from plants, two approaches can be chosen: either via impedance or via biopotentials. The latter might be considered more sensitive to subtle physiological changes, thus instead of a polygraph, we have chosen to measure with an EEG device. After experimenting with various setups, the final setup of the EEG measurement system was as follows: Active and ground electrodes were placed on the leaves of the ficus tree while the reference electrode was put into the soil (Fig. 1). A proper understanding of how EEG works [3] and what kind of signals it sends to the outcome, is crucial for the correct setting of the plant experiments as well as for the interpretation of the measured signals.
We presented various disturbances to the plant, both contact and non-contact. The contact ones included induction of “pain” by pressure, leaf cutting, or flame. With a sufficiently strong impact directly on the plant, an immediate reaction in the measured signal was present. It depended on the distance of the point of impact and the placement of the electrodes. But that was no surprise or mystery, just a direct consequence of changes in the system’s electrical parameters.
Thus we moved to the application of non-contact stimuli: A person was approaching, stretching his hand towards the plant while keeping distance from it; stepping into the lab with positive or negative speech, or just with different thoughts regarding praising or harming the plant. No reactions were obtained. Until… Suddenly, a signal event occurred on the laptop display (Fig. 2). We stood frozen for a while. We have got it! In fact, it really seemed to be a demonstration of the plant’s mysterious reactions, as there was like a 1 or 2-meter distance from acting human.
After calming down our excitations and recapping our knowledge and experience regarding technical problems with such a sensitive measurements, we had to repeat the experimental setup of this activity while changing some of its parameters. Namely the distance of the approaching palms, and their speed. In this way, together with the use of appropriate measurement methodology and systematic approach, we finally had to conclude that unfortunately, it might be just a measurement artefact. In a situation with a lot of noise in the signal, these kinds of artefacts are usually caused by changes in surrounding environmental influences due to parasitic impedances, or interferences from nearby objects representing subtle changes in electrical fields.
Quite often, investigators who perform these or similar “edge” experiments might be lacking deeper professional background. Eventually, even being a specialist in relevant fields, possessing some kind of burden in the form of predetermined belief, can cause being fooled by oneself. Or, in a better case, just being puzzled. The reason is, that sensitive measurement itself, together with output signals is quite a complex issue.
Moreover, in 2016 I reviewed and supported a secondary school student project entitled “Changes of plants electrical activity during touch stimulation and mechanical harm”, that qualified for the national round of the competition “Czech secondary school research activity”. They have also measured biopotentials with electromyographic device. I have no permission to publish the original work, but for those who want to get some insight into kind of technical objections, I can present here my review (in Slovak). It demonstrates, how the interpretation of any anomalous behaviour might often be explained just by artefacts.
As a final lesson, we have learnt, that what looks or is promoted as being mysterious or supernatural, will often turn to be explicable by natural means and up-to-date knowledge.
Final verdict: No plant consciousness, issues of complex measurement.
References:
[1] https://en.wikipedia.org/wiki/Cleve_Backster
[2] Cleve Backster, Primary Perception: Biocommunication with plants, living foods, and human cells (2003) White Rose Millennium Press
[3] Teplan, M.: Fundamentals of EEG measurement. In: Measurement Science Review, Section 2, Vol. 2, 2002.