Influence of premorbid personality and location of lesion on emotional expression

The neural basis of optimism and pessimism

Our survival and wellness require a balance between optimism and pessimism. Undue pessimism makes life miserable; however, excessive optimism can lead to dangerously risky behaviors. A review and synthesis of the literature on the neurophysiology subserving these two worldviews suggests that optimism and pessimism are differentially associated with the two cerebral hemispheres. High self-esteem, a cheerful attitude that tends to look at the positive aspects of a given situation, as well as an optimistic belief in a bright future are associated with physiological activity in the left-hemisphere (LH). In contrast, a gloomy viewpoint, an inclination to focus on the negative part and exaggerate its significance, low self-esteem as well as a pessimistic view on what the future holds are interlinked with neurophysiological processes in the right-hemisphere (RH). This hemispheric asymmetry in mediating optimistic and pessimistic outlooks is rooted in several biological and functional differences between the two hemispheres. The RH mediation of a watchful and inhibitive mode weaves a sense of insecurity that generates and supports pessimistic thought patterns. Conversely, the LH mediation of an active mode and the positive feedback it receives through its motor dexterity breed a sense of confidence in one's ability to manage life's challenges, and optimism about the future.

Depression and the hyperactive right-hemisphere

Depression is associated with an inter-hemispheric imbalance; a hyperactive right-hemisphere (RH) and a relatively hypoactive left-hemisphere (LH). Nevertheless, the underlying mechanisms which can explain why depression is associated with a RH dominance remain elusive. This article points out the potential links between functional cerebral asymmetries and specific symptoms and features of depression. There is evidence that the RH is selectively involved in processing negative emotions, pessimistic thoughts and unconstructive thinking styles--all which comprise the cognitive phenomenology of depression and in turn contribute to the elevated anxiety, stress and pain associated with the illness. Additionally, the RH mediates vigilance and arousal which may explain the sleep disturbances often reported in depression. The RH had also been linked with self-reflection, accounting for the tendency of depressed individuals to withdraw from their external environments and focus attention inward. Physiologically, RH activation is associated with hyprecortisolemia, which contributes to the deterioration of the immune system functioning and puts depressed patients at a greater risk of developing other illnesses, accounting for depression's high comorbidity with other diseases. Conversely, the LH is specifically involved in processing pleasurable experiences, and its relative attenuation is in line with the symptoms of anhedonia that characterize depression. The LH is also relatively more involved in decision-making processes, accounting for the indecisiveness that is often accompanied with depression.

Emotional responses during unilateral amobarbital anesthesia: differential hemispheric contributions?

OBJECTIVES

To explore (1) effects of test and subject variables in determining euphoric and dysphoric responses during unilateral amobarbital anesthesia and (2) which cerebral areas contribute to the emotional responses.

METHOD

Incidence of euphoric and dysphoric reactions during left- and right-sided amobarbital anesthesia of the internal carotid artery (ICA) and selective anesthesia of the middle cerebral (MCA) and the posterior cerebral (PCA) artery was recorded. The sample comprised 270 Norwegians (6-61 years), and a total of 562 injections were performed under conditions endeavoring to calm down the patients.

RESULTS

The overall incidence of observed emotional responses during ICA anesthesia was 21.5%, euphoric reactions being about 10 times more frequent than dysphoric. The incidence of euphoric reactions, however, was not significantly higher under right- than under left-sided anesthesia, and dysphoric reactions were not more frequent under left- than under right-sided anesthesia. Indeed, 13 patients showed elevated mood under both right- and left-sided anesthesia. Anesthesia of the territories of ICA and MCA gave rise to similar results, while no cases of mood change were observed under selective PCA anesthesia.

CONCLUSION

It is concluded that unilateral amobarbital anesthesia as such, irrespective of side, may trigger both euphoric and dysphoric responses. The relative frequency obtained is influenced importantly both by the emotional responsiveness of the subjects and the emotional climate of the test situation. Finally, it is suggested that brain regions supplied by the PCA contribute less to modulation of euphoric and dysphoric responses than those supplied by the MCA or the ICA.

Hemispheric specialization in emotion: attention, arousal, and EEG activation in unilateral temporal lobe epilepsy

To investigate the neural processing of emotion in right and left temporal lobe epilepsy (TLE), we monitored EEG during neutral and emotionally positive and negative auditory stimulation. Left TLE patients displayed increased right lateralization and a negative emotional stimulus rating bias, while right TLE patients did not. This EEG arousal and negative affect may reflect deactivated inhibition of the right hemisphere, symptomatically expressed as arousal and anxiety. Failure to increase lateralization to emotional stimuli in right TLE may reflect compromised emotional attention/arousal centers in the right hemisphere. Results support a two-dimensional theory of the neural processing of emotion.

Hemispheric language dominance in children demonstrated by functional magnetic resonance imaging

The objective of this study was to demonstrate hemispheric language dominance in normal children. Fifteen normal children were evaluated with functional magnetic resonance imaging (MRI) using an age-related silent word spelling paradigm. The data were analyzed with the cross-correlation method, and lateralization indices were calculated in language regions as determined by Talairach coordinates. Activation foci were detected in the left inferior frontal area and were strongly lateralized, with language lateralization indices of 0.74 +/- 0.21 (age 7-12 years, nine subjects), and 0.79 +/- 0.18 (13-18 years, six subjects). The indices were similar to those for adults (0.83 +/- 0.21, four subjects). Our study established that language is strongly lateralized to the left hemisphere in children as young as 7 years of age.