Pert's work over the past 20 years, which she describes in her book Molecules of Emotion, has led her to conclude that chemicals called neuropeptides, which are produced and have receptors throughout the brain and body, are the biochemical correlates of emotions. For Pert, the distribution of peptide receptors throughout the body is of critical importance, and she challenges the long-held assumption in traditional neuroscience that emotions are an entirely brain-based phenomenon. More recently, Pert has used the implications of her research on emotion to make claims about the nature of gut feelings. Damasio, in his book Descartes' Error and other publications, focuses primarily on how we make decisions, and his unique contribution is his theory that emotions play a central role in appropriate decision-making. His somatic marker hypothesis, which will be thoroughly discussed, clearly implicates the body as a source of emotional input crucial to the decision-making process. Yet, he definitely does view the brain as the location of integration between emotional inputs and input about the characteristics of the external situation. Furthermore, he maintains that after initial somatic input is linked with a specific type of situation, phenomenon such as gut feelings can arise through a closed circuit within the brain, in other words in the absence of input from or output to the body. As we will see, though there is a great deal of complementary ground covered by these two theorists, they disagree about the issue of whether gut feelings can exist in the absence of input from and output to the body.
We begin with an examination of Candace Pert's contribution (1). Stepping back from everything that Pert has written or that has been written about her theories, the theme that underlies Pert's work is the intimate connection between the brain and the body. While the belief in a "mind-body" connection goes back many centuries, Pert and her colleagues at the National Institute of Mental Health(NIMH) were pioneers in discovering a molecular basis for this link. The underlying idea is that "the mind and body constantly chatter back and forth using a vocabulary of biochemicals, the detectable results of which is the full range of human emotions" (2). Pert, herself, discloses that at the outset of her work some 20 years ago, she took it as a given that emotions were in the brain. She now asserts that they are in the body as well (3). So what, we ask, has accounted for Pert's change of perspective? The major scientific discovery that has influenced Pert is the finding that neuropeptides and their receptors, once believed to exist only in the brain, are now known to manifest themselves throughout the body as well. The underlying implication of this finding, according to Pert, is that the neural, hormonal, gastrointestinal, and immune systems, all equipped with neuropeptide receptors and the capabilities to produce neuropeptides, are set up in a network, and are able to communicate with one another via peptides and messenger-specific peptide receptors(4). In this view, emotions are the biochemical messengers that connect the major systems of the body into one unit which Pert calls the "body-mind". Thus, they are cellular signals at the nexus between matter and mind, which are implicated in the process of translating information into physical reality (5).
Pert's theories about the nature of emotion are rooted in a wealth of experimental research. She is best-known for discovering the opiate receptor and subsequently mapping the brain's opiate receptors (though Solomon Snyder, her then-advisor at Hopkins credits himself with the discovery, (6)). Yet, in recent years, she has also become somewhat of a guru for the less mainstream mind-body movement and alternative medicine. Pert is now drawing upon some of her scientifically-validated findings in order to explain other phenomenon, and it seems to me that sometimes she goes too far. She asserts that since neuropeptides and their receptors exist in the body, it leads to the conclusion that the mind is located in the body, in the same sense that the mind is in the brain (5). I think that in this statement, Pert makes an unfounded leap from emotions, which she has convincingly shown have a basis in the body, to feelings. For example, Pert discusses the nature of gut feelings based on her findings about emotion. She argues that the entire lining of the gastrointestinal tract, from the esophagus to the large intestine is lined with cells that contain neuropeptides and receptors. Therefore, she argues that it is the stimulation of these peripheral receptors that account for the fact that we feel our emotions in this part of our body (7). Hence, from Pert's perspective, one cannot have gut feelings without the release of neuropeptide molecules that activate somatic receptors in the peripheral body. This is an important point, the validity of which is challenged by Damasio.
Antonio Damasio, in essence, argues that the feeling that we refer to when we talk about a gut feeling is not the actual neuropeptide chemicals that Pert designates as "molecules of emotion", but rather the pattern of activity that these chemicals stimulate in the brain. The important implication, as we will see, is that this pattern of activity that initially was formed as a result of an emotional input from the body can be regenerated through a neural process Damasio calls the "as if" loop without implicating the peripheral somatic body. But let's back up for a minute, give some background on Damasio's perspective, and describe what he coins the "somatic marker hypothesis", a theory that, in many respects, does incorporate a lot of Pert's work. The initial motivation for Damasio's theory grew out of a clinical finding about patients with damage to the ventromedial prefrontal lobes. Damasio found that such patients had clear deficits in their ability to experience feelings, along with a co-occurring difficulty making good personal and social decisions. In other words, the brain-damaged patients, it seems, did not experience gut feelings that they can draw upon in the decision-making process, a finding that implicates the ventromedial prefrontal lobe in the ability to experience gut feelings.
According to Damasio's "somatic marker hypothesis", there is an important process that must occur in order to set the stage for the phenomenon of gut feelings, and this process most definitely implicates the somatic state of the body. Damasio sounds much like Pert when he asserts that "emotions bubble up from the chemical chatter between brain and body, hinging on such visceral changes as an elevated heart rate or hormonal activity" (8). According to Damasio, structures in the prefrontal cortex called the ventromedial cortices, learn associations between types of complex situations and emotional states that accompany these different situations. In the brain, the somatic state results from emotional input from the body eliciting an activity pattern in the somatosensory cortex(9) & (10). Up to this point, Damasio and Perts' theories do not conflict. Pert's findings about neuropeptides and their receptors simply adds depth to the understanding of the physiology behind the transmission of emotional states from the periphery to the brain. Damasio's theory goes on to explain that, at a later point in time, when a similar situation occurs, the ventromedial cortices, which earlier had established a connection between the type of situation and the type of somatic state, trigger the reactivation of the somatosensory pattern that encoded the relevant somatic state. This reactivation can occur in one of two ways, and it is the latter that Pert would, most definitely, take issue with. The first way is through a "body loop", meaning that soma physically change in reaction to activation by the prefrontal cortex, and the resulting changes are sent to somatosensory cortices. The second possible path is via an "as if" loop in which the reactivation signals are transmitted directly to the somatosensory cortex (i.e. they bypass the body), which then takes on the appropriate pattern. When the image that results from the somatosensory pattern is adjoined with the images that activated the somatic state and which depict a scenario of future outcome, the somatosensory pattern marks the scenario as good or bad. In this way, the somatic state can serve as an alarm signal or an incentive signal, both of which can be referred to as gut feelings (9) & (10).
In reflecting on Damasio's theory, it seems important to point out what implications the idea of bypassing the body has in terms of somatic experience. What it does mean is that the neuronal signals that activate the somatosensory cortex all occur within the brain in the absence of input from or output to the body. However, this does not mean that one would not have the feeling of sensation in regions of the body such as the stomach. After all, the somatosensory cortex that is being stimulated is topographically organized such that when certain parts of it are activated it can give the feeling of sensation in the stomach (a.k.a. a literal "gut" feeling), even though receptors in the stomach are not actually being stimulated.
So, having considered the work of Pert and Damasio, where does this leave us in terms of understanding gut feelings? I first want to point out a problematic aspect of Pert's thinking, which I believe narrows her conception of how a gut feeling can arise. As I touched on before, I think that at times in her writing and in statements she is quoted to have said, Pert mistakenly equates emotions and feelings. Pert's extremely important scientific research on the existence of neuropeptide receptors throughout the body refuted the long-held belief that emotions are the property of the brain. Yet, somewhere along the line, after establishing that the body is a prerequisite for emotion, Pert began to argue that feeling cannot occur without simultaneous input from the body (11). This is a gigantic jump that merges the concepts of emotion and feeling in a way that I maintain is inappropriate. The fact that there are densely-packed neuropeptide receptors in the stomach means that emotional information can be exchanged there, yet it does not mean that the feeling of that emotion occurs at those receptors. According to Damasio, the distinction between an emotion and a feeling is that an emotion "a collection of changes in body state" while feeling an emotion is "the experience of such changes in juxtaposition to the mental images that initiated the cycle" (12). Damasio also asserts that "not all feelings originate in emotions" (12). It becomes clear now why Pert would take issue with the "as if" loop. Her theory, which is so centered on the neuropeptides (the so-called "molecules of emotion") activating receptors, does not allow for the possibility that feelings could result from the reactivation of already established somatosensory patterns through neural rather than somatic means. I maintain that while her theory that emotions are based in chemical interactions between somatic and neural cells is well-founded, she mistakenly applies the same theory to feelings. It seems clear to me that Pert's main goal is to demonstrate that the body is intimately involved in feelings. Therefore, the existence of an "as if" loop would strike a severe blow to her theory because it is proof that gut feelings can sometimes be "all in your head". This said, we must be careful not to blindly accept the existence of the "as if" loop presented by Damasio.
In the literature that I read by Damasio, he gives multiple examples of research findings that support his somatic marker hypothesis, yet it all focuses on the path whereby the "body loop", activated by the prefrontal cortex, reactivates a pattern of activity in the somatosensory cortex. I would be interested to see research studies that offer experimental evidence for the "as if" loop. Given what I know about the nervous system, his "as if" loop hypothesis seems plausible, but unless he can show that there is in fact no input from or output to the body involved in the process, researchers such as Pert have a strong basis to challenge his hypothesis.
2) Cassel Research Centre , see section on "Where Feelings are Born"
3)Dept h of change, suffering, and the growth of love, See section on "The Unity of Our Being"
4) Healing Arts Report , See section on Science Report
5) Pert, Candace. Molecules of Emotion. Simon and Schuster Ltd. 1998
7) Implications of Molecules of Emotion
8) Does the Brain Listen to Gut Feelings?
9) The Prefrontal Cortex and Damasio's Somatic Marker Hypothesis
10) Damasio, Antonio. "On Some Functions of the Human Prefrontal Cortex"
12) Damasio, Antonio. Descartes' Error. Avon Books. 1994.