The superior temporal sulcus is a long trench, called a sulcus, in the temporal lobe. In essence, this region is vital to social competence. To a significant extent, the anterior portion of this sulcus is primarily involved in the processing of speech. The posterior portion is more involved in an array of other tasks, including facial processing, motion processing, the integration of audio and vision information, as well as theory of mind--or deciphering the beliefs and perspectives of other people. The precise role of this region depends on which other areas in the cortex are activated as well (Hein & Knight, 2008).
The superior temporal sulcus is in the temporal lobe--like a long trough or trench that separates two ridges: the superior temporal gyrus and the middle temporal gyrus. The superior temporal sulcus has been shown to form bidirectional connections to many regions of the brain. These regions include most parts of the prefrontal regions and the premotor areas as well as the parietal cortex and mesial temporal region, as first shown in rhesus monkeys (see Seltzer & Pandya, 1989, 1994).
Many studies indicate the superior temporal sulcus is vital to theory of mind. Theory of mind refers to the capacity of individuals to recognize that every person experiences unique desires, beliefs, and perspectives, depending on their own experience. For example, to assess theory of mind in children, a box, which usually contains Smarties or some other candy, is presented. The children are first asked to guess the contents of this box. They usually guess the box contains Smarties. Next, they are informed the box actually contains pencils. Finally, they are asked to indicate what another person, who did not observe the pencils, would assume is contained in the box. Children who have developed a theory of mind recognize this other person would presume the box contains Smarties. That is, these children realize their own beliefs might diverge from the assumptions of someone else (see Gopnik & Astington, 1988).
When people undertake tasks that assess theory of mind, using tasks that are similar to the questions about the box of Smarties, the superior temporal sulcus, coupled with the medial prefrontal regions, are activated, as shown by fMRI studies (e.g., Kobayashi, Glover, & Elise, 2007& Voellm, Taylor, Richardson, Corcoran, Stirling, McKie, et al., 2006). According to Hein and Knight (2008), the role of this sulcus might depend on which other regions are activated. Specifically, the posterior superior temporal sulcus may be especially germane to theory of mind, enabling individuals to differentiate their own beliefs from the assumption of other people, when the medial prefrontal cortex is also activated. However, the same region may offer other functions when combined with different brain areas.
The superior temporal sulcus seems to be crucial to social interactions in general. In particular, this region seems to process social cues. For example, activations of the neurons in this region is sometimes sensitive to the eye gaze of another person as well as other subtle cues (see Perrett, Hietanen, Oram, & Benson, 1992). Hence, this region can ascertain the location in which other people are directing their attention.
As outlined by Hein and Knight (2008), a variety of fMRI studies have examined whether or not the superior temporal sulcus is involved in the processing of faces. Some studies, for example, have investigated whether or not this region is more likely to be activated when people observed faces rather than other images, such as scrambled pictures or houses (Haxby, Ungerleider, Clark, Schouten, Hoffman, & Martin, 1999& Hoffman & Haxby, 2000& Ishai, Schmidt, & Boesiger, 2005). In these studies, the faces were stationary and not moving or dynamic.
As these studies showed, facial processing activates the superior temporal sulcus. Specifically, the posterior, but not the anterior, portion is activated. This role in facial processing is consistent with the assumption that perhaps the superior temporal sulcus is integral to social competence.
Several regions of the brain, including the superior temporal sulcus, particularly the anterior ventral bank (O' Doherty, Winston, Critchley, Perrett, Burt, & Dolan, 2003) as well as the medial orbitofrontal cortex (Kranz & Ishai, 2006), seem to be involved in the perception of facial attractiveness of potential mates. That is, when people interact or observe a person of the opposite sex whose face is attractive, rather than unattractive, activation of these regions increases.
The superior temporal sulcus is also vital to the processing of speech, consistent with the key role of this region in social interactions. A variety of studies have examined whether activation of the superior temporal sulcus depends on whether participants are exposed to speech as opposed to other sounds (e.g., Binder et al., 2000& Rimol, Specht, Weis, Savoy, & Hugdahl, 2005& Uppenkamp, Johnsrude, Norris, Marslen-Wilson, & Patterson, 2006). In these studies, only verbal, rather visual, information was presented, dissociating speech processing from other capacities, like the ability to integrate different modalities.
These studies indicate that processing of speech increases activation of the anterior superior temporal sulcus. Indeed, speech processing seems to be one of the main functions of the anterior superior temporal sulcus.
As a variety of studies have shown, the superior temporal sulcus seems to facilitate the integration of visual and auditory information (Beauchamp, Lee, Argall, & Martin, 2004& Calvert, Hansen, Iversen, & Brammer, 2001& Taylor, Moss, Stamatakis, & Tyler, 2006& Van Atteveldt, Formisano, Goebel, & Blomert, 2004). This capacity can enhance speech processing, because facial cues, such as lip movement, can be utilized to amplify muffled speech.
As these fMRI studies have demonstrated, some neurons in the posterior superior temporal sulcus are more likely to be activated when both visual and auditory information is presented. This sensitivity to visual and auditory information persists even if the sounds are unrelated to speech.
As Park, Gu, Kang, Shin, Choi, Lee, & Kwon (2010) showed, the superior temporal sulcus, together with the inferior frontal sulcus and amygdala, seems to integrate emotional information rather than neutral information from other sources. That is, these regions are especially likely to be activated when individuals need to process both visual and verbal emotional information at the same time, such as a person with an angry or happy face and angry or happy tone. Integration of emotional information from multiple senses is vital: Such integration can identify the emotional state of someone else more rapidly. Integration can also uncover discrepancies between the facial expression and voice of people, implying that further processing is warranted. This role of the superior temporal sulcus is consistent with the notion that perhaps this region underpins social competence.
Specifically, in this study, participants were exposed to a series of verbal recordings, video recordings of a face without sound, or video recordings of a face with sound while the person is speaking. These verbal or video recordings depicted happiness, anger, or no emotion. The task of participants was merely to indicate the gender of this person. Finally, fMRI was recorded to determine which brain regions were activated differentially in each condition.
The superior temporal sulcus, together with the inferior frontal sulcus and amygdala, were especially likely to be activated when the participants were exposed to either happy or angry information both verbally and visually. These regions, thus, may integrate emotional information from different senses.
Other regions were also more likely to be activated when participants were exposed to emotional information from both the eyes and ears. However, the sensitivity of these regions was restricted to either happiness or anger but not both. The left middle temporal gyrus integrated happy, but not angry, information from these senses--as did the inferior parietal lobe, hippocampus, cuneus, and anterior cingulate. Other regions integrated only angry information from these senses, including the posterior cingulate, fusiform gyrus, and cerebellum.
The superior temporal sulcus seems to be involved in processing the motion of people or objects. In some studies, participants watch people. However, these people are obscured. Instead, only lights attached to their main joints are visible. The participants recognize that people are moving but cannot process specific features such as faces. Therefore, these studies determine whether the superior temporal sulcus processes motion processing independent of facial processing.
For example, in several studies, participants watch either these light displays of people or random displays of lights (Grossman & Blake, 2002& Peuskens, Vanrie, Verfaille, & Orban, 2005& Vaina, Solomon, Chowdhury, Sinha, & Belliveau, 2001). As fMRI imaging showed, processing the movement of people seems to coincide with activation of both the anterior and posterior superior temporal sulcus in the left hemisphere but only the posterior superior temporal sulcus in the right hemisphere (for a review, see Hein & Knight, 2008).
Conceivably, the role of these regions partly depends on which other regions are activated at the same time. The superior temporal sulcus may underpin the processing of motion especially when the pre-motor areas are activated as well (Hein & Knight, 2008).
A study, conducted by Molenberghs, Brander, Mattingley, and Cunnington (2010), has also shown the superior temporal sulcus enables individuals to connect the actions of other people to their own actions. For instance, in one study, some participants merely watched an action, such as a person hammering a nail. Other participants imitated this action. Furthermore, some participants then initiated this action in response to a specific word. Finally, some participants merely executed an action they selected.
The superior temporal sulcus, as well as the left supramarginal gyrus, left superior parietal lobule, and left dorsal premotor area, were activated in all four conditions. Interestingly, the superior temporal sulcus was especially active when an action was imitated. Conceivably, this region enables individuals to translate representations of an action, performed by someone else, into the actions they need to undertake. Again, the capacity of individuals to differentiate themselves from other people, also vital to theory of mind tasks, seems germane to this activity as well.
To some extent, the superior temporal sulcus seems to underpin this capacity in individuals to recognize they chose some course of action themselves. Indeed, the superior temporal sulcus seems to underpin self criticism (see also Frith & Frith, 1999). Again, the superior temporal sulcus may enable individuals to differentiate themselves from other people, vital to social interaction and theory of mind tasks.
Nevertheless, according to the Yomogida, Sugiura, Sassa, Wakusawa, Sekiguchi, Fukushima, Takeuchi, Horie, Sato, & Kawashima (2010), the superior temporal sulcus may not underpin this sense of agency. To clarify, a sense of agency is a feeling in individuals that they generated some action themselves. If the sensory feedback of a movement matches the expectations of an intended action, individuals will feel a sense of agency. In contrast, if the sensory feedback of a movement diverges from the expectations of an intended action, individuals will feel some other force might have influenced their behaviour.
In one study, participants played a video game. A character appeared on a screen. Sometimes, the movement of this character was erratic, diverging from expectations. In some, but not all, conditions, participants attempted to controll the movement of this character. Erratic movement of the character affected activation of the superior temporal sulcus. However, unlike some other regions, such as the supplementary motor area, left cerebellum, right posterior parietal cortex, and right extrastriate body area, activation of the superior temporal sulcus did not depend on whether the participants were able to control the character. Therefore, the superior temporal sulcus may process deviations from expectations but not necessarily agency.
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Last Update: 7/18/2016