Process modified Stroop test reveals vmPFC not only emotionally bound

efore discussing the role of the orbitofrontal cortex, I might refer the reader to my other posts throughout the semester, as to the absence of one-to-one structural-functional relationships of the brain, otherwise termed polymodality or association (see also Zillmer, Spiers, & Culbertson, 2008). Second, it is important to consider that the various constructs as used in the materials to which I refer in this article are consistently revised through iterative scientific methodology. Lastly, making light of the nature of both the aforementioned, it is vital to remember that emotional behavior is a very complex construct and there are even more complexities when science works to attribute complexities in causal relationships. With these in mind, I integrate various sources and examine a very interesting article I found that challenges and “invites the hypothesis that the ventromedial prefrontal cortex may not be as 'silent' with respect to mediating cognitive functions [and only involved in emotional regulation] as previously thought (Cato, Delis, Abildskov, & Bigler, 2004, p. 464).

The ventro-medial prefrontal cortex (vmPFC – located at the base of the anterior frontal lobes, adjacent to midline), which includes the medial orbitofrontal cortex (OFC) and the subgenual anterior cingulate cortex (ACC), is involved in regulating emotionally driven behavior (Carlson, 2010, p. 375). Important to note are the connections from the temporal cortex, the olfactory system, and the amygdala (memory, emotion, limbic system) (p. 375). According to Carlson (2010) and others, it is clear that the vmPFC is responsible for inhibiting emotional behavior, largely through the study of "natural experiments," case material, and neuroimaging (Larner & Leach, 2002, p. 26).

One such natural experiment is the legendary case of Phineas Gage. Injured by a railroad tamping iron through the cheek and out the top of his skull, Phineas Gage was never the same after his traumatic injury – his marked dispositional change, from irreverence, capriciousness, profanity and irresponsibleness (Larner & Leach, 2002, p. 26), to an inability to carry out plans, whimsicality, and thoughtlessness of others (Carlson, 2010, p. 376) are today recognized as hallmarks of OFC injury that are sometimes referred to as “pseudopsychopathy” (Larner & Leach, 2002, p. 26) or “acquired sociopathy,” differing from antisocial personality disorder (APD) by the ability to feel remorse and lack of vicious planning involved in APD (Zillmer, et al., 2008, p. 256).

Other issues commonly found in OFC injuries, prominent in large lesions, are environmental dependency syndrome. These are stimulus bound behaviors like utilization behavior (hand a patient pajamas, and regardless of context, they may undress and put them on), grasp reflex, and manual groping (p. 256). However, Carlson (2010), like many others, claim that vmPFC injury typically leave cognitive functions intact, following the usual syndrome of emotional dysregulation (and its correlates), going so far as to state: “[t]here was no relationship between cognitive abilities and real world competencies, which strongly suggests that emotional problems lie at the base of the real-world difficulties [a construct referring to judgment, planning, social inappropriateness, and financial and occupational status] exhibited by people with vmPFC damage” (p. 377). However, both Zillmer and colleagues (2008) – who bring in theoretical notions regarding impaired empathy and somatic marking (i.e., impaired automatic tagging of situations that help with response selection; typically assessed neuropsychologically with the gambling task (Bechera and colleagues as cited in Zillmer, et al., 2008, pp. 256-7) and one article I found, refuted this notion, showing that “[o]n the one hand, patients with VM-PFD may truly be spared from cognitive deficits and suffer from isolated emotional and behavioral impairments. Another possibility is that VM-PFD does lead to cognitive deficits in addition to emotional-behavioral dysfunction, and traditional neuropsychological tests have generally failed to identify such deficits in these patients" (Cato, et al., 2004, p. 454).

Cato’s study revealed that through the use of more sensitive neuropsychological testing that “the bifurcation of prefrontal cortex into two functional subregions [long recognized as a method to help parse a structure-function relationship and to reductively study the PFC], with higher-level cognitive functions mediated primarily by dorsolateral prefrontal regions [dlPFC] and emotional-behavioral regulation subserved primarily by ventromedial prefrontal cortex [vmPFC], may be inaccurate” (p. 464). The testing uses “process-oriented neuropsychological measures designed to quantify subtle cognitive deficits that may exist over and above the emotional or behavioral changes typically found in VM-PFD [ventro-medial prefrontal damage] patients (p. 454) and included two commonalities “(1) task demands that tapped multiple executive functions simultaneously, including cognitive shifting; and (2) scoring systems that went beyond the traditional measures of time-to-completion or level of accuracy, and also quantified and normed error types” (p. 463). This is important because their results followed a patient “whose VM-PFC damage was remarkably similar to that of Phineas Gage,” with all the typical symptom presentation and whose most salient problems related to emotional-behavioral regulation. The difference was that upon testing, Cato's patient was found to have marked cognitive deficits (p. 464).

Cato and colleagues argued that the cognitive functions may be organized in the frontal lobes along a continuum, where higher level processes are located most anterior (i.e., within the vmPFC), and simpler executive controls were more susceptible not to the vmPFC per se, but more concentrated in the dlPFC (p. 464). Their conclusion was that a process oriented approach to neuropsychological testing (adding a task switching task to the Stroop test) revealed deficits post vmPFC lesion (p. 464). In their words: “the highest levels of cognitive and emotional integration may occur in ventromedial prefrontal cortex, which, when compromised, may affect an individual’s ability to perform multilevel executive-function and memory tasks...[illustrating] how the use of multilevel executive-function tasks (e.g., inhibition plus switching) may capture higher-level deficits that may otherwise be missed by traditional procedures” (p. 464).

In conclusion, it is clear that biopsychology has much to learn by way of ongoing and iterative study of the human brain, whether in Gageian naturalistic experiment, animal modeling, computer simulation, or imaging. As the evidence builds, including those seminal 19th century studies, a clearer picture of the complexity of structure-function polymodal association becomes important to consider. Certainly, without the intriguing case of Phineas Gage and the Cato study’s patient, these associations might never be fully understood. I find it quite marvelous that with the triangulation of data from tests like the Stroop (plus switching task), MRIs, and historical records, the field advances to include ever more complexity and subtlety that gives future patients, their families, and caregivers, more information and possibilities for hope than ever before.



References

Carlson, N. (2010). Physiology of behavior, (10th ed.). Boston: Allyn & Bacon.

Cato, M., Delis, D., Abildskov, T., & Bigler, E. (2004). Assessing the elusive cognitive deficits associated with ventromedial prefrontal damage: A case of a modern-day Phineas Gage. Journal of the International Neuropsychological Society, 10(3), 453-465. doi:10.1017/S1355617704103123

Larner, A. & Leach, J. (2002). Phineas Gage and the beginnings of neuropsychology. ACNR, 2(3), 26.

Zillmer, E., Spiers, M., & Culbertson, W. (2008). Principles of neuropsychology, (2nd ed.). Belmont, CA: Thomson Wadsworth.