Thursday, July 11, 2013

Tobias Grossmann - The Role of the Medial Prefrontal Cortex in Early Social Cognition


The medial prefrontal cortex (mPFC) is primarily involved in processing, representing, and integrating social and affective information. We know now that it is one of the last brain areas to be fully developed (with some now suggesting that it can continue to develop throughout the lifespan), reaching maturity for many people in their late 30s.

A 2001 study by Gusnard, Akbudak, Shulman, and Raichle, looked at the role of mPFC in self-referential mental activity.
[The] dorsal and ventral MPFC are differentially influenced by attention demanding tasks and explicitly self-referential tasks. The presence of self-referential mental activity appears to be associated with increases from the baseline in dorsal MPFC. Reductions in ventral MPFC occurred consistent with the fact that attention-demanding tasks attenuate emotional processing. We posit that both self-referential mental activity and emotional processing represent elements of the default state as represented by activity in MPFC. We suggest that a useful way to explore the neurobiology of the self is to explore the nature of default state activity.
One of the primary roles of the mPFC is "executive function," as outlined in this section from the Wikipedia entry on the frontal cortex.

Executive functions


The original studies of Fuster and of Goldman-Rakic emphasized the fundamental ability of the prefrontal cortex to represent information not currently in the environment, and the central role of this function in creating the "mental sketch pad". Goldman-Rakic spoke of how this representational knowledge was used to intelligently guide thought, action, and emotion, including the inhibition of inappropriate thoughts, distractions, actions, and feelings.[25] In this way, working memory can be seen as fundamental to attention and behavioral inhibition. Fuster speaks of how this prefrontal ability allows the wedding of past to future, allowing both cross-temporal and cross-modal associations in the creation of goal-directed, perception-action cycles.[26] This ability to represent underlies all other higher executive functions.

Shimamura proposed Dynamic Filtering Theory to describe the role of the prefrontal cortex in executive functions. The prefrontal cortex is presumed to act as a high-level gating or filtering mechanism that enhances goal-directed activations and inhibits irrelevant activations. This filtering mechanism enables executive control at various levels of processing, including selecting, maintaining, updating, and rerouting activations. It has also been used to explain emotional regulation.[27]

Miller and Cohen proposed an Integrative Theory of Prefrontal Cortex Function, that arises from the original work of Goldman-Rakic and Fuster. The two theorize that “cognitive control stems from the active maintenance of patterns of activity in the prefrontal cortex that represents goals and means to achieve them. They provide bias signals to other brain structures whose net effect is to guide the flow of activity along neural pathways that establish the proper mappings between inputs, internal states, and outputs needed to perform a given task”.[28] In essence, the two theorize that the prefrontal cortex guides the inputs and connections, which allows for cognitive control of our actions.

The prefrontal cortex is of significant importance when top-down processing is needed. Top-down processing by definition is when behavior is guided by internal states or intentions. According to the two, “The PFC is critical in situations when the mappings between sensory inputs, thoughts, and actions either are weakly established relative to other existing ones or are rapidly changing”.[28] An example of this can be portrayed in the Wisconsin Card Sorting Test (WCST). Subjects engaging in this task are instructed to sort cards according to the shape, color, or number of symbols appearing on them. The thought is that any given card can be associated with a number of actions and no single stimulus-response mapping will work. Human subjects with PFC damage are able to sort the card in the initial simple tasks, but unable to do so as the rules of classification change.

Miller and Cohen conclude that the implications of their theory can explain how much of a role the PFC has in guiding control of cognitive actions. In the researchers' own words, they claim that, “depending on their target of influence, representations in the PFC can function variously as attentional templates, rules, or goals by providing top-down bias signals to other parts of the brain that guide the flow of activity along the pathways needed to perform a task”.[28]

Experimental data indicate a role for the prefrontal cortex in mediating normal sleep physiology, dreaming and sleep-deprivation phenomena.[29]

When analyzing and thinking about attributes of other individuals, the medial prefrontal cortex is activated. However, it is not activated when contemplating about the characteristics of inanimate objects.[30] As of recent, researchers have used neuroimaging techniques to find that along with the basal ganglia, the prefrontal cortex is involved with learning exemplars, which is part of theexemplar theory, one of the three main ways our mind categorizes things. The exemplar theory states that we categorize judgements by comparing it to a similar past experience within our stored memories. [31]
With all of this background, we still know very little about the mPFC in infants, how it develops and what roles it plays in affect and early social cognition. This new study looks at what is known about the mPFC in infants.

The role of medial prefrontal cortex in early social cognition



Tobias Grossmann
Early Social Development Group, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany

One major function of our brain is to enable us to behave with respect to socially relevant information. Much research on how the adult human brain processes the social world has shown that there is a network of specific brain areas, also called the social brain, preferentially involved during social cognition. Among the specific brain areas involved in the adult social brain, functional activity in prefrontal cortex (PFC), particularly the medial prefrontal cortex (mPFC), is of special importance for human social cognition and behavior. However, from a developmental perspective, it has long been thought that PFC is functionally silent during infancy (first year of life), and until recently, little was known about the role of PFC in the early development of social cognition. I shall present an emerging body of recent neuroimaging studies with infants that provide evidence that mPFC exhibits functional activation much earlier than previously thought, suggesting that the mPFC is involved in social information processing from early in life. This review will highlight work examining infant mPFC function across a range of social contexts. The reviewed findings will illustrate that the human brain is fundamentally adapted to develop within a social context.

Full Citation: 
Grossmann T. (2013, May 6). The role of medial prefrontal cortex in early social cognition. Frontiers in Human Neuroscience; 7:340. doi: 10.3389/fnhum.2013.00340

Introduction


Humans possess a number of higher cognitive skills vital for language, reasoning, planning, and complex social behavior. The prefrontal cortex (PFC) can be seen as the neural substrate that underpins much of this higher cognition (Wood and Grafman, 2003). PFC refers to the regions of the cerebral cortex that are anterior to premotor cortex and the supplementary motor area (Zelazo and Müller, 2002). Based on its neuroanatomical connections, the PFC can be broadly divided into two sections: (a) the medial PFC (mPFC) and (b) the lateral PFC (lPFC) (Wood and Grafman, 2003; Fuster, 2008). The mPFC includes the medial portions of Brodmann areas (BA) 9–12, and BA 25, and has reciprocal connections with brain regions that are implicated in emotional processing (amygdala), memory (hippocampus) and higher-order sensory regions (within temporal cortex) (for more detailed information see, Wood and Grafman, 2003Fuster, 2008). The lPFC includes the lateral portions of Brodmann areas (BA) 9–12, BA 44, 45 and BA 46, and has reciprocal connections with brain regions that are implicated in motor control (basal ganglia, premotor cortex, supplementary motor area), performance monitoring (cingulate cortex) and higher-order sensory processing (within temporal and parietal cortex) (for more detailed information see, Wood and Grafman, 2003; Fuster, 2008).

Critically, the distinction between lPFC and mPFC in neuroanatomical terms maps onto general differences in brain function. Namely, while mPFC is thought to be mainly involved in processing, representing and integrating social and affective information, lPFC is thought to support cognitive control process (Wood and Grafman, 2003; Fuster, 2008). This general functional distinction between mPFC and lPFC can already be seen early in development during infancy (Grossmann, 2013), thus representing a developmentally continuous organization principle of PFC function. As far as brain function is concerned, mPFC has been shown to play a fundamental role in a wide range of social cognitive abilities such as self-reflection, person perception, and theory of mind/mentalizing (Amodio and Frith, 2006). This involvement of mPFC in social cognition and interaction has lead to the notion that mPFC serves as a key region in understanding self and others (Frith and Frith, 2006). Although this is not the focus of this review, it should be noted that apart from its implication in social cognitive functions in adults, mPFC has been shown to be more generally involved in a number of processes related to decision making in adults (e.g., Heekeren et al., 2008). In particular, most recently, a unifying model has been proposed that views mPFC as a region concerned with learning and predicting the likely outcomes of actions (Alexander and Brown, 2011).

Only very little is known concerning the role of the mPFC in the development of social cognition. This is particularly true for the earliest steps of postnatal development, namely during infancy (the first year of life). Addressing the question of whether mPFC plays a role in infant social cognition and if it does, to theorize about what role this might be is the goal of this review. Such a look at early social cognition during infancy through the lenses of social neuroscience is critical because it allows us (a) to understand the nature and developmental origins of mPFC function, and (b) to close a gap between the extensive behavioral work showing rather sophisticated infant social cognitive skills (Spelke and Kinzler, 2007Woodward, 2009; Baillargeon et al., 2010) and the social neuroscience work with adults studying mature mPFC functioning (Amodio and Frith, 2006Lieberman, 2006).

That mPFC plays an important role in the development of social cognition is evident in work examining mPFC lesions. For example, there is work comparing early onset (during infancy) and adult onset lesions to mPFC (Anderson et al., 1999). This work shows that, despite typical basic cognitive abilities, patients with mPFC lesions had severely impaired social behavior. More specifically, regardless of when the mPFC lesion had occurred, there are symptoms shared across patients with mPFC damage, including an insensitivity to future consequences of actions, defective autonomic responses to punishment contingencies, and failure to respond to interventions that would change behavior (Anderson et al., 1999). Critically, this study revealed that over and above the shared symptomatology, acquired damage to mPFC during infancy had a much more severe impact on social functioning signified by striking defects concerning social and moral reasoning, leading to a syndrome that closely resembled psychopathy. In this study, it was found that early onset damage to mPFC was related to antisocial behaviors such as stealing, violence against persons and property, severe impairment of social-moral reasoning and verbal generation of responses to social situations. Specifically, in adults with early onset lesions to mPFC, moral reasoning was conducted at a much lower level than expected by their age, such that moral dilemmas were mainly approached from an egocentric perspective characterized by avoiding punishment. Furthermore, early onset damage of mPFC was related to a limited consideration of the emotional implications of one owns behavior for others and much fewer responses generated to resolve interpersonal conflict. This suggests that mPFC plays a critical role in the acquisition of social and moral behaviors already early during ontogeny. It further suggests that in contrast to many other brain regions where damage and especially damage early in ontogeny can be compensated (Thomas and Johnson, 2008), mPFC appears to be less plastic or more vulnerable. This in turn indicates that there might be a sensitive period in development during which mPFC is required to develop and learn socially and morally appropriate behaviors. Even though the study of patients with lesions to the mPFC is of great importance in illuminating mPFC function, patients with circumscribed mPFC lesions acquired during infancy, as reported by Anderson and colleagues (1999), are extremely rare and can hence only provide limited insights into these early stages of developing mPFC function. It is therefore all the more important to employ functional neuroimaging to shed light on the development of mPFC function during infancy if we wish to better understand its role in early social cognition.

Recent advances in applying functional imaging technology to infants, specifically, the advent of using functional near-infrared spectroscopy (fNIRS) has made it possible to study the infant brain at work. fNIRS is an optical imaging method that measures hemodynamic responses from cortical regions, permitting for the localization of brain activation (Lloyd-Fox et al., 2010). Other neuroimaging techniques that are well established in adults are limited in their use with infants because of methodological concerns. For example, functional magnetic resonance imaging (fMRI) requires the participant to remain very still and exposes them to a noisy environment. Although fMRI has been used with infants, this work is restricted to the study of sleeping, sedated or very young infants. The method of fNIRS is better suited for infant research because it can accommodate a good degree of movement from the infants, enabling them to sit upright on their parent's lap and behave relatively freely while watching or listening to certain stimuli. In addition, unlike fMRI, fNIRS systems are portable. Finally, despite its inferior spatial resolution also in terms of obtaining responses from deeper (subcortical) brain structures, fNIRS, like fMRI, measures localized patterns of hemodynamic responses in cortical regions, thus allowing for a comparison of infant fNIRS data with adult fMRI data. In the last decade, there has been a surge of fNIRS studies with infants, including a number of studies that have looked at PFC activation during a wide range of experimental tasks (for review, see Grossmann, 2013). In the following sections, I shall review the available experimental evidence that implicate mPFC in infant social cognition. This review is aimed at providing an overview of the range of social contexts during which infants employ the mPFC. The review of the empirical work is organized according to the two main sensory modalities (audition and vision) in which social stimuli were presented to infants. Following the presentation of the experimental evidence, I will discuss a number of issues that arise from these studies. Finally, based on these findings, I will outline an account of what role mPFC plays in the early development of social cognition during infancy.
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