A selective and critical review of neuropsychological deficits and the frontal lobes

Presumptions about the functions of the frontal lobes, and the sensitivity and specificity of certain tests to measure frontal lobe functions, are having a substantial influence on both clinical and research conclusions. In this paper the authors examine the details of the studies that have contributed to these presumptions, and find that the evidence to support these conclusions is weak. A detailed evaluation of the evidence relating to the Wisconsin Card Sorting Test and the Thurstone Word Fluency Test is also presented. Finally, the development of the belief that frontal lobe functions can be specifically measured is reviewed. The authors of this paper conclude that the bewildering array of deficits attributed to frontal lesions still seems to prevail.     

Eye movements of monkey observers viewing vocalizing conspecifics

Primates, including humans, communicate using facial expressions, vocalizations and often a combination of the two modalities. For humans, such bimodal integration is best exemplified by speech-reading - humans readily use facial cues to enhance speech comprehension, particularly in noisy environments. Studies of the eye movement patterns of human speech-readers have revealed, unexpectedly, that they predominantly fixate on the eye region of the face as opposed to the mouth. Here, we tested the evolutionary basis for such a behavioral strategy by examining the eye movements of rhesus monkeys observers as they viewed vocalizing conspecifics. Under a variety of listening conditions, we found that rhesus monkeys predominantly focused on the eye region versus the mouth and that fixations on the mouth were tightly correlated with the onset of mouth movements. These eye movement patterns of rhesus monkeys are strikingly similar to those reported for humans observing the visual components of speech. The data therefore suggest that the sensorimotor strategies underlying bimodal speech perception may have a homologous counterpart in a closely related primate ancestor.     

Frontal-Lobe Involvement in Spatial Memory: Evidence from PET,fMRI, and Lesion Studies

Many studies have identified the prefrontal cortex as the brain area that is critical for spatial memory, both in humans and in other primates. Other studies, however, have failed to establish this relation. Therefore, the aim of this paper was to review the literature regarding the role of the human prefrontal lobe in spatial memory. This was done by examining the evidence obtained from neuropsychological patients and from studies using brain-imaging techniques (PET and fMRI). Evidence supporting the notion that the prefrontal cortex is extensively involved in spatial working memory was found. The majority of these studies, however, suggests that frontal-lobe involvement is not related to the type of material that is being processed (e.g., spatial vs. nonspatial), but to process-specific functions, such as encoding and retrieval. Theoretically, these functions could be linked to the central executive within Baddeley's working-memory model, or to recent theories that emphasize the various processes that play a role in working memory. Also, methodological issues were discussed. Further research is needed to enhance our understanding of the precise interaction of domain-specific and general processes.     

The nature and treatment of stuttering as revealed by fMRI A within- and between-group comparison

This article reviews some of our recent functional magnetic resonance imaging (fMRI) studies of stuttering. Using event-related fMRI experiments, we investigated brain activation during speech production. Results of three studies comparing persons who stutter (PWS) and persons who do not stutter (PWNS) are outlined. Their findings point to a region in the right frontal operculum (RFO) that was consistently implicated in stuttering. During overt reading and before fluency shaping therapy, PWS showed higher and more distributed neuronal activation than PWNS. Immediately after therapy differential activations were even more distributed and left sided. They extended to frontal, temporal, and parietal regions, anterior cingulate, insula, and putamen. These over-activations were slightly reduced and again more right sided two years after therapy. Left frontal deactivations remained stable over two years of observation, and therefore possibly indicate a dysfunction. After therapy, we noted higher activations in persons who stutter moderately than in those who stutter severely. These activations might reflect patterns of compensation. We discuss why these findings suggest that fluency-inducing techniques might synchronize a disturbed signal transmission between auditory, speech motor planning, and motor areas.

Educational objectives: The reader will learn about and be able to: (1) identify regions of brain activations and deactivations specific for PWS; (2) describe brain activation changes induced by fluency shaping therapy; and (3) discuss the correlation between stuttering severity and brain activation.     

The Elusive Nature of Executive Functions: A Review of our Current Understanding

Executive functions include abilities of goal formation, planning, carrying out goal-directed plans, and effective performance. This article aims at reviewing some of the current knowledge surrounding executive functioning and presenting the contrasting views regarding this concept. The neural substrates of the executive system are examined as well as the evolution of executive functioning, from development to decline. There is clear evidence of the vulnerability of executive functions to the effects of age over lifespan. The first executive function to emerge in children is the ability to inhibit overlearned behavior and the last to appear is verbal fluency. Inhibition of irrelevant information seems to decline earlier than set shifting and verbal fluency during senescence. The sequential progression and decline of these functions has been paralleled with the anatomical changes of the frontal lobe and its connections with other brain areas. Generalization of the results presented here are limited due to methodological differences across studies. Analysis of these differences is presented and suggestions for future research are offered.     

Beyond Fear Emotional Memory Mechanisms in the Human Brain

ABSTRACT— Neurobiological accounts of emotional memory have been derived largely from animal models investigating the encoding and retention of memories for events that signal threat. This literature has implicated the amygdala, a structure in the brain's temporal lobe, in the learning and consolidation of fear memories. Its role in fear conditioning has been confirmed, but the human amygdala also interacts with cortical regions to mediate other aspects of emotional memory. These include the encoding and consolidation of pleasant and unpleasant arousing events into long-term memory, the narrowing of focus on central emotional information, the retrieval of prior emotional events and contexts, and the subjective experience of recollection and emotional intensity during retrieval. Along with other mechanisms that do not involve the amygdala, these functions ensure that significant life events leave a lasting impression in memory.     

Mental number line disruption in a right-neglect patient after a left-hemisphere stroke

A right-neglect patient with focal left-hemisphere damage to the posterior superior parietal lobe was assessed for numerical knowledge and tested on the bisection of numerical intervals and visual lines. The semantic and verbal knowledge of numbers was preserved, whereas the performance in numerical tasks that strongly emphasize the visuo-spatial layout of numbers (e.g. number bisection) was impaired. The behavioral pattern of error in the two bisection tasks mirrored the one previously described in left-neglect patients. In other words, our patient misplaced the subjective midpoint (numerical or visual) to the left as function of the interval size. These data, paired with the patient's lesion site are strictly consistent with the tripartite organization of number-related processes in the parietal lobes as proposed by Dehaene and colleagues. According to these authors, the posterior superior parietal lobe on both hemispheres underpins the attentional orientation on the putative mental number line, the horizontal segment of the intraparietal sulcus is bilaterally related to the semantic of the numerical domain, whereas the left angular gyrus subserves the verbal knowledge of numbers. In summary, our results suggest that the processes involved in the navigation along the mental number line, which are related to the parietal mechanisms for spatial attention, and the processes involved in the semantic and verbal knowledge of numbers, are dissociable.     

Children’s Affect Expression and Frontal EEG Asymmetry: Transactional Associations with Mothers’ Depressive Symptoms

Although parents and children are thought to influence one another's affect and behavior, few studies have examined the direction of effects from children to parents, particularly with respect to parental psychopathology. We tested the hypothesis that children's affective characteristics are associated with the course of mothers' depressive symptoms. Children's affect expression was observed during a series of mother-child interaction tasks, and children's resting frontal electroencephalogram (EEG) asymmetry was assessed in a psychophysiology laboratory. Mothers' depressive symptoms were assessed at two time points, approximately one year apart, at the mother-child interaction visits. Depressive symptoms increased over time for mothers with a history of childhood-onset depression whose children exhibited right frontal EEG asymmetry. Depressive symptoms were associated with high child negative affect at both time points for mothers whose children exhibited right frontal EEG asymmetry. Cross-lagged models with a subset of participants provided some evidence of both parent-to-child and child-to-parent directions of effects. Findings suggest that akin to other interpersonal stressors, children's affective characteristics may contribute to maternal depressive symptoms.     

Connectivity among semantic associates: an fMRI study of semantic priming

Semantic priming refers to a reduction in the reaction time to identify or make a judgment about a stimulus that has been immediately preceded by a semantically related word or picture and is thought to result from a partial overlap in the semantic associates of the two words. A semantic priming lexical decision task using spoken words was presented in event-related fMRI and behavioral paradigms. Word pairs varied in terms of semantic relatedness and the connectivity between associates. Thirteen right-handed subjects underwent fMRI imaging and 10 additional subjects were tested in a behavioral version of the semantic priming task. It was hypothesized priming would be greatest, reaction time fastest, and cortical activation reduced the most for related word pairs of high connectivity, followed by related word pairs of low connectivity, and then by unrelated word pairs. Behavioral and fMRI results confirmed these predictions. fMRI activity located primarily in bilateral posterior superior and middle temporal regions showed modulation by connectivity and relatedness. The results suggest that these regions are involved in semantic processing.