Chiao-Yun Chen

Control of prepotent responses by the superior medial frontal cortex.

The inhibitory control of prepotent action is vital for appropriate behaviour. An example of the importance of such control can be seen in the inhibition of aggressive behavior, deficits in which may have broader consequences for society. Many studies have related lesions or the under-development of the prefrontal cortex to inefficiency of inhibitory control. Here we used transcranial magnetic stimulation and a stop-signal task, which occasionally requires the inhibition of a prepotent motor response, to investigate the role of pre-supplementary motor area (Pre-SMA) in inhibitory control. While no effects were seen on the ability to generate responses, TMS delivered over the Pre-SMA disrupted the ability to respond to a stop signal. These results are the first to establish a casual link between Pre-SMA and inhibitory control in normal subjects. The understanding of the underlying mechanisms of inhibitory control may lead to clearer understanding of the neural basis of inappropriate behaviour.

Neural correlates of impulsive-violent behavior: an event-related potential study

Impulsive-violent offenders are often less capable of controlling their behavior. A cued Go/No-go task was used to test the hypothesis that impulsive-violent behavior reflects a deficit in the ability to inhibit prepotent responses and could be reflected in the measurement of event-related potentials. Results showed that the amplitudes of the N2 component at Fz reflected different degrees of inhibition in impulsive-violent offenders compared with matched controls. The N2 amplitude (No-go minus Go) was significantly lower in the impulsive-violent offenders than in matched controls. The amplitude of N2 increased when effort was required to withhold the Go intention. A smaller N2 amplitude was seen in offenders, suggesting difficulties with inhibition of prepotent behavior.

Inhibitory control and the frontal eye fields

Inhibitory control mechanisms are important in a range of behaviors to prevent execution of motor acts which, having been planned, are no longer necessary. Ready examples of this can be seen in a range of sports, such as cricket and baseball, where the choice between execution or inhibition of a bat swing must be made in a brief time interval. The role of the FEFs, an area typically described in relation to eye movement functions but also involved in visual processes, was investigated in an inhibitory control task using transcranial magnetic stimulation (TMS). A stop signal task with manual responses was used, providing measures of impulsivity and inhibitory control. TMS over FEF had no effect on response generation (impulsivity, indexed by go signal RT) but disrupted inhibitory control (indexed by stop signal RT). This is the first demonstration of a role for FEF in this type of task in normal subjects in a task which did not require eye movements and complements previous TMS findings of roles for pre-SMA and inferior frontal gyrus (IFG) in inhibitory control.

Time pressure leads to inhibitory control deficits in impulsive violent offenders

Impulsive violent criminal behavior is often ascribed to problems with behavioral control. Such behavior could be a consequence of stronger pre-potent responses or a failure of inhibitory control. A countermanding task which allows dissociation of these two processes was used to examine whether impulsive violent offenders were found to exhibit impaired inhibitory control. An experiment with a time restriction on responding was performed to effectively limit the ability of the subjects to strategically control their error rate. The results showed that the performance of the impulsive violent offenders was only impaired in the time pressure condition. These findings suggest that impulsive violent behavior may be linked to abnormal modulation of the frontal cortical areas, areas thought to be involved in response inhibition by negative feedback or emotional responses, rather than frontal dysfunction per se.

Motor empathy is a consequence of misattribution of sensory information in observers

Human behavior depends crucially on the ability to interact with others and empathy has a critical role in enabling this to occur effectively. This can be an unconscious process and based on natural instinct and inner imitation (Montag et al., 2008) responding to observed and executed actions (Newman-Norlund et al., 2007). Motor empathy relating to painful stimuli is argued to occur via the mirror system in motor areas (Rizzolatti and Luppino, 2001). Here we investigated the effects of the location of emotional information on the responses of this system. Motor evoked potential (MEP) amplitudes from the right first dorsal interosseus (FDI) muscle in the hand elicited by single pulses of transcranial magnetic stimulation (TMS) delivered over the left motor cortex were measured while participants observed a video of a needle entering a hand over the FDI muscle, representing a painful experience for others. To maintain subjects’ internal representation across different viewing distances, we used the same size of hand stimuli both in peripersonal and extrapersonal space. We found a reduced MEP response, indicative of inhibition of the corticospinal system, only for stimuli presented in peripersonal space and not in extrapersonal space. This empathy response only occurring for near space stimuli suggests that it may be a consequence of misidentification of sensory information as being directly related to the observer. A follow up experiment confirmed that the effect was not a consequence of the size of the stimuli presented, in agreement with the importance of the near space/far space boundary for misattribution of body related information. This is consistent with the idea that empathy is, at least partially, a consequence of misattribution of perceptual information relating to another to the observer and that pain perception is modulated by the nature of perception of the pain.

Assessment of psychiatric disorders among sex offenders: Prevalence and associations with criminal history

BACKGROUND Much of the research on the prevalence of psychiatric disorders among sex offenders has been conducted in the USA or Europe. Less is known about it in other regions, particularly in Asia. AIMS The objective of this study is to determine the prevalence of psychiatric disorders among sex offenders in Taiwan and their associations with offender characteristics and criminal history. METHODS Participants were randomly selected from men serving sentences in Taiwans prison for serious sex offenders. Consenting men were assessed using the structured clinical interviews for DSM-IV-TR Axis I and II disorders. Demographics and criminal history were also recorded. RESULTS Over two-thirds of the 68 participants met criteria for one or more lifetime Axis I disorders, and nearly 60% met criteria for one or more Axis II disorder. The higher the number of Axis I and cluster B personality disorders, the higher was the total number of convictions. CONCLUSIONS Our study adds to the literature that suggests that psychiatric assessment is likely to have an important role in the management and treatment of sex offenders. The finding that multiple disorders are common in this group and associated with more convictions for sex offences suggests that failure to include psychiatric assessment in planning the management of sex offenders may increase the risk of recidivism.

Inefficiency of post-error adjustment in impulsive violent offenders

Criminal offenders who show repeated impulsive violent behavior are often described as having impairments in both inhibitory control and error processing. A sample of such offenders was compared with controls using event-related potentials recorded during the performance of a combined flanker and stop-signal task with the aim of investigating the underlying mechanisms that may contribute toward such violent behavior by indexing conflict monitoring, error detection, and post-error processing. The results obtained indicated lower amplitude of the stop-signal N2 component for successfully inhibited trials, reflecting different degrees of inhibition in impulsive violent offenders, as well as a reduced Pe component over the parietal area, an indication of reduced awareness of errors. This is consistent with the behavioral data indicating a lack of post-error slowing compared with the control group. This suggests that these offenders have problems with error awareness, subjective error assessment processes, and the adjustment of future behavior.

Posterior parietal cortex and visuospatial control in near and far space

Neuropsychological studies of patients with visuospatial neglect have shown differences in perceptual deficits for information in near space (i.e. near to the body) and information in far space. It has been suggested that among the many areas of the human brain, a number of areas are associated with a set of spatial maps specialized for visuospatial control related to this spatial distinction. This paper reviews how parietal cortex is thought to be involved in visuospatial neglect in relation to its control of visuospatial attention in the left and right visual fields and at different viewing distances. In particular, the importance of regions of the parietal cortex in the pathogenesis of neglect and in spatial attention and perception is discussed. Parietal cortex may control different distributions of attention across space by allocating specific attentional resources in near and far space while also showing attentional asymmetry across visual fields. Transcranial magnetic stimulation (TMS) as a technique offers the advantage of examining the direct behavioral effect of disruption of many of these areas with excellent temporal and spatial resolution. We discuss the use of TMS and the insights it may offer regarding the roles of these areas in neglect as well as normal visuospatial perception.

Sport, time pressure, and cognitive performance

Sport participation, fitness, and expertise have been associated with a range of cognitive benefits in a range of populations but both the factors that confer such benefits and the nature of the resulting changes are relatively unclear. Additionally, the interactions between time pressure and cognitive performance for these groups is little studied. Using a flanker task, which measures the ability to selectively process information, and with different time limits for responding, we investigated the differences in performance for participants in (1) an unpredictable, open-skill sport (volleyball), (2) an exercise group engaged in predictable, closed-skill sports (running, swimming), and (3) nonsporting controls. Analysis by means of a drift diffusion analysis of response times was used to characterize the nature of any differences. Volleyball players were more accurate than controls and the exercise group, particularly for shorter time limits for responding, as well as tending to respond more quickly. Drift diffusion model analysis suggested that better performance by the volleyball group was due to factors such as stimulus encoding or motor programming and execution rather than decision making. Trends in the pattern of data seen also suggest less noisy cognitive processing (rather than greater efficiency) and should be further investigated.

Attentional biases to emotion in impulsive and instrumental violent offenders: an event-related potential study

Background: Interpersonal violent behavior is often induced by extreme emotional states but the effects of emotional stimuli on this behavior remain poorly understood. Aim: We compared the effects of emotional stimuli on behavior in individuals with a history of impulsive or instrumental violence to test for either general problems in processing of emotional stimuli or problems in disengagement from this type of information. Methods: Behavioral and electrophysiological data were collected using emotional stimuli preceding a Posner Cuing Task. Results: Impulsive violent individuals showed more attentional resource allocation to angry faces whereas instrumental violent individuals attended less to sad faces. Electrophysiological measures showed there were differences in attentional allocation leading to differences when disengaging from invalid emotional cues, rather than a pattern indicating differences in early processing in extrastriate cortex. Conclusions: Different emotion–attention problems are seen in impulsive and instrumental violent offenders due to abnormalities in disengaging attention from specific types of emotional content.