A team of researchers at the Massachusetts Institute of Technology (MIT) has proposed that vertebrates may have developed the neural pathways necessary for consciousness around 500 million years ago. The researchers are exploring how ancient brain structures, such as the thalamus and medulla, contribute to conscious experiences, such as the sensation of thirst.
Daniel Freeman, PhD, an MIT scientist involved in the study, emphasized the importance of defining consciousness to better understand its location in the brain. He suggested that some interpretations of consciousness link it to cognition, while others associate it with metacognition—the ability to think about oneself. In Freeman’s view, primitive neural circuitry from early vertebrates underlies conscious experiences across all vertebrates, from fish to humans.
The researchers aim to identify a finite list of conscious experiences and map the corresponding brain areas. They are employing transcranial focused ultrasound (tFUS), a technique that allows non-invasive stimulation of neurons in the deep brain. This method utilizes low-level ultrasound to send mechanical sound waves into the brain while patients are awake, enabling scientists to gauge their sensations in real-time.
During experiments, stimulation of a specific area in the upper brain stem elicited reports of heightened motivation from patients. Freeman noted that the stimulation invoked feelings such as, “I feel really like I am ready to go!” He also remarked on the distinct differences in patient responses to stimulation in deeper brain structures compared to the outer brain structures.
In a related study at Stanford University, researchers observed that stimulating the hypothalamus led patients to experience intense emotions, such as shame and grief, which seemed to draw on deep-seated memories. One patient equated the emotion to a significant loss she experienced.
Freeman’s team is particularly focused on understanding the neural basis of thirst. They believe that a specific cell cluster in the hypothalamus is responsible for this conscious experience. If these cells are damaged, subjects do not feel thirst even when saline solutions are administered, indicating the complexity of consciousness in humans versus other vertebrates.
Freeman further explained that the intricate thoughts humans engage in arise from fundamental experiences generated in the deep brain, which are processed by the outer cortex. He acknowledges that while his perspective is one of several, it aligns with findings from other scientists studying consciousness-related signals in brain areas like the thalamus.
Additionally, research at Ludwig-Maximilians-University Munich highlighted a previously unnoticed rapid activity pattern in the human thalamus during waking hours and REM sleep, suggesting it may signal consciousness. This rapid neuronal oscillation, occurring at frequencies between 20 to 45 Hertz, vanishes during non-REM sleep, reinforcing the connection between consciousness and certain brain activities.
The findings raise further questions about consciousness across different species, including invertebrates like octopuses, which exhibit intelligent behaviors without a conventional brain structure. Freeman acknowledged the complexity of understanding consciousness in such cases, stating, “I have to throw my hands up and say, ‘I don’t know.’”
As research continues, the MIT team hopes to map the conscious experiences of vertebrates using tFUS, potentially advancing the understanding of this complex phenomenon in the animal kingdom.
