Social functioning has been defined as “the ability to construct representations of the relations between oneself and others, and to use those representations flexibly to guide social behavior” (Adolphs, 2001). Certainly, complex behaviors like personality and social conduct are derived from multiple distributed networks of functional circuits. Though the evidence for specific brain-behavior relationships in the area of social cognition is still under development, the main brain regions thought to be involved in social functioning this include the temporal lobes (TL), the orbitofrontal cortex (OFC), the dorsomedial frontal cortex (dmPFC), and the dorsolateral frontal cortex (dlPFC).
The temporal lobes, particularly in the non-dominant hemisphere, are essential for accurate perception and interpretation of social communication. TL regions are responsible for recognizing familiar faces and facial emotions, interpreting voice prosody, and understanding a person’s intentions and emotions from their body posture, gestures, and movements. There is also some evidence that the anterior TL may be involved in precipitating emotional empathy. Damage to this region short circuits the ability to correctly perceive the other’s nonverbal signals and evaluate their communicative intent, which can in turn disrupt higher order social cognitive processing performed in the frontal lobes.
Inaccurate evaluation of the reward or punishment value of social information is probably the mechanism by which some patients with frontal lobe injury fail to adhere to social norms, and this evaluation is thought to be performed by the OFC. The failure to rapidly translate social information into altered behavior may also be responsible for some OFC-related social deficits. In behavioral terms, patients with damage to the OFC, particularly in the right hemisphere, show a pattern of behavioral dyscontrol that may involve
- either emotional blunting and emotional lability, including an insensitivity to others emotions,
- deficient decision-making, including poor social and non-social judgment, lack of self-monitoring, and/or inflexibility, and
- deficient goal-directed behavior, including apathy, disinhibition, task impersistence, and general disorganization.
The dorsomedial portions of the frontal lobes, including the anterior cingulate, paracingulate, superior frontal gyrus, and frontal pole (BA 9/10) appear to be involved in higher-level social cognition. There is increasing evidence that the complex processes of self-monitoring and taking the perspective of others are highly interdependent, and are both mediated by dmPFC structures.
The lateral frontal lobe areas mediate conventional executive skills such as planning, sequencing, inhibition, generation, working memory, and abstract reasoning, all of which directly impact our ability to perform complex reasoning about social information. The capacity to intentionally regulate, organize, and plan our own behavior, as well as to deliberate about the behaviors of others, is partly mediated by these dlPFC functions.
Many aspects of emotional processing occur in subcortical structures, including the amygdala, hypothalamus, and multiple regions in the brainstem in emotional processing (Panksepp, 1998). The way that the higher neocortical structures interact with these regions is less clear, but both human and animal studies have revealed an extensive network of regions in the frontal and temporal lobes involved in emotional and social processing.
The amygdala appears crucial for learning the association between a previously neutral stimulus (such as a light or tone, called a conditioned stimulus, or CS) and a biologically relevant reward or punishment (e.g. food or shock, both unconditioned stimuli, or USs), and for altering behavior to match these new associations (for an excellent review see (Cardinal, Parkinson, Hall, & Everitt, 2002). In humans, amygdala damage also leads to impaired recognition of specific facial expressions of emotion, with fear being the most affected (Adolphs et al., 1999). Another important structure is the nucleus accumbens (Acb), in the ventral striatum, which appears to mediate as well as modulate some amygdala dependent responses. Several other cerebral structures, including the orbital frontal cortex (OFC), the anterior cingulate cortex (ACC) and the anterior temporal neocortex, play an important role in emotional processing. OFC, in addition to the amygdala, plays a role in conditioned responding.In humans with OFC lesions, experimental “gambling” paradigms reveal an inability to inhibit the drive to choose stimuli leading to large immediate rewards, even though it becomes increasingly clear that these choices not advantageous in the long run (Bechara, Tranel, Damasio, & Damasio, 1996).
Lesion studies indicate that ACC plays a role in emotion recognition (Hornak et al., 2003). Perhaps related to ACC damage, the ability of patients with FTD to recognize negative emotions (i.e., anger, sadness, disgust) in others, facial emotional expressions is impaired, particularly when the emotions are exhibited on static faces (Keane et al. 2002; Lavenu, et al. 1999; Lough, et al. 2005). In two cross-sectional studies, fear recognition was also shown to be impaired (Lough et al. 2005; Rosen et al. 2004b). A test of identifying vocal emotion yielded similar results: angry and sad voices were poorly identified, but there were additional deficits in recognizing the sounds of happiness or surprise (Keane, et al. 2002). In patients with SD, atrophy in the right anterior temporal cortex is associated with impaired recognition of emotional facial expressions (Rosen et al., 2006).
In general, lesions studies in humans have suggested that the right hemisphere plays a dominant role in emotional processing. Patients with injury to the right hemisphere are sometimes emotionally flat, and have difficulty understanding and expressing the normal emotional signals in the voice (variations in pitch, speed, etc., called prosody) and in facial gestures (Ross, 1997). In patients with the temporal variant of frontotemporal dementia, emotional blunting is observed primarily in association with right temporal degeneration (Miller, Chang, Mena, Boone, & Lesser, 1993).
The frontal lobes, which make up 40% of the human cerebral cortex, are greatly expanded in humans compared to non-human primates (Stuss & Benson, 1986). Far from a monolithic structure with a single purpose, the frontal lobes are divided into multiple structurally, physiologically and functionally distinct regions with important functions related to movement, motor planning, language, intelligence, working memory, generation, inhibition, alternating sequences, drive, emotion, self-awareness, insight, and personality.
The cognitive functions most commonly attributed to the frontal lobes are higher order or executive processes which involve the organization of more basic cerebral processes to promote efficient task performance and establishment of associations beyond basic representation of incoming sensory information. Examples of important cognitive functions of the frontal lobes include abstraction, inhibition, and facilitating the shifting of cognitive sets (Fuster, 1997; Luria, 1966). Also, the frontal lobes play a key role in attention, memory (particularly working memory) and language.
Efficient, successful completion of tasks requires the ability to avoid distraction and to maintain mental effort on a given task until it is complete. Patients with frontal lobe damage are often impaired in these functions, leading them to be distractible, disorganized and very inefficient (Zakzanis, 1998).
Often we are required to maintain two or more tasks in mind simultaneously, and constantly shift between them. In addition, it is sometimes necessary to suppress the impulse to perform certain tasks to reach our goals. These functions are significantly impaired with frontal lobe injury (Luria, 1966) with profound consequences.
Many of the functions described above are associated with the dorsolateral portions of the frontal lobes. Generally, verbal tasks disproportionately tap left frontal functions, while visual tasks are more likely to use the right frontal lobe. Inhibition tasks seem to rely upon both the dorsolateral and the orbital frontal region. A variety of disorders with selective subcortical involvement, like progressive supranuclear palsy, disconnect the frontal lobes from subcortical activation and lead to frontal lobe neuropsychological syndromes.