Co-Planar Stereotaxic Atlas of the Human Brain—3-Dimensional Proportional System: An Approach to Cerebral Imaging, J. Talairach, P. Tournoux. Georg Thieme Verlag, New York (1988), 122 pp., 130 figs. DM 268

Bartlett viewed thinking as a high level skill exhibiting ballistic properties that he called its “point of no return”. This paper explores one aspect of cognition through the use of a simple model...

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Orienting of attention

The two basic phenomena that define the problem of visual attention can be illustrated in a simple example. Consider the arrays shown in each panel of Figure 1. In a typical experiment, before the arrays were presented, subjects would be asked to report letters appearing in one color (targets, here black letters), and to disregard letters in the other color (nontargets, here white letters). The array would then be briefly flashed, and the subjects, without any opportunity for eye movements, would give their report. The display mimics our. usual cluttered visual environment: It contains one or more objects that are relevant to current behavior, along with others that are irrelevant. The first basic phenomenon is limited capacity for processing information. At any given time, only a small amount of the information available on the retina can be processed and used in the control of behavior. Subjectively, giving attention to any one target leaves less available for others. In Figure 1, the probability of reporting the target letter N is much lower with two accompa­ nying targets (Figure la) than with none (Figure Ib). The second basic phenomenon is selectivity-the ability to filter out un­ wanted information. Subjectively, one is aware of attended stimuli and largely unaware of unattended ones. Correspondingly, accuracy in identifying an attended stimulus may be independent of the number of nontargets in a display (Figure la vs Ie) (see Bundesen 1990, Duncan 1980).

Neural Mechanisms of Selective Visual Attention

: The concept of attention as central to human performance extends back to the start of experimental psychology, yet even a few years ago, it would not have been possible to outline in even a preliminary form a functional anatomy of the human attentional system. New developments in neuroscience have opened the study of higher cognition to physiological analysis, and have revealed a system of anatomical areas that appear to be basic to the selection of information for focal (conscious) processing. The importance of attention is its unique role in connecting the mental level of description of processes used in cognitive science with the anatomical level common in neuroscience. Sperry describes the central role that mental concepts play in understanding brain function. As is the case for sensory and motor systems of the brain, our knowledge of the anatomy of attention is incomplete. Nevertheless, we can now begin to identify some principles of organization that allow attention to function as a unified system for the control of mental processing. Although many of our points are still speculative and controversial, we believe they constitute a basis for more detailed studies of attention from a cognitive-neuroscience viewpoint. Perhaps even more important for furthering future studies, multiple methods of mental chronometry, brain lesions, electrophysiology, and several types of neuro-imaging have converged on common findings.

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The Attention System of the Human Brain

Attention deficit hyperactivity disorder (ADHD) comprises a deficit in behavioral inhibition. A theoretical model is constructed that links inhibition to 4 executive neuropsychological functions that appear to depend on it for their effective execution: (a) working memory, (b) self-regulation of affect-motivation-arousal, (c) internalization of speech, and (d) reconstitution (behavioral analysis and synthesis). Extended to ADHD, the model predicts that ADHD should be associated with secondary impairments in these 4 executive abilities and the motor control they afford. The author reviews evidence for each of these domains of functioning and finds it to be strongest for deficits in behavioral inhibition, working memory, regulation of motivation, and motor control in those with ADHD. Although the model is promising as a potential theory of self-control and ADHD, far more research is required to evaluate its merits and the many predictions it makes about ADHD.

/pdf/behavioral-inhibition-sustained-attention-and-executive-3s4ta68l66.pdf

Behavioral inhibition, sustained attention, and executive functions: Constructing a unifying theory of ADHD.

Neglect is a failure to report, respond, or orient to contralateral stimuli that is not caused by an elemental sensorimotor deficit. Subtypes of neglect are distinguished by input (attentional) or output (intentional) demands, the distribution (personal, spatial, and representational), and the means of eliciting the signs (unilateral or bilateral stimuli). In this article we discuss how to assess patients for neglect, the pathophysiology of neglect, and the treatment of neglect.

Neglect and related disorders

This article and its accompanying editorial have been selected for the ANESTHESIOLOGYCME Program. After reading both articles, go to http://www.asahq.org/journal-cme to take the test and apply for Category 1 credit. Complete instructions may be found in the CME section at the back of this issue. Background: The authors designed a prospective longitudinal study to investigate the hypothesis that advancing age is a risk factor for postoperative cognitive dysfunction (POCD) after major noncardiac surgery and the impact of POCD on mortality in the first year after surgery. Methods: One thousand sixty-four patients aged 18 yr or older completed neuropsychological tests before surgery, at hospital discharge, and 3 months after surgery. Patients were categorized as young (18‐39 yr), middle-aged (40‐59 yr), or elderly (60 yr or older). At 1 yr after surgery, patients were contacted to determine their survival status. Results: At hospital discharge, POCD was present in 117 (36.6%) young, 112 (30.4%) middle-aged, and 138 (41.4%) elderly patients. There was a significant difference between all age groups and the age-matched control subjects (P < 0.001). At 3 months after surgery, POCD was present in 16 (5.7%) young, 19 (5.6%) middle-aged, and 39 (12.7%) elderly patients. At this time point, the prevalence of cognitive dysfunction was similar between age-matched controls and young and middle-aged patients but significantly higher in elderly patients compared to elderly control subjects (P < 0.001). The independent risk factors for POCD at 3 months after surgery were increasing age, lower educational level, a history of previous cerebral vascular accident with no residual impairment, and POCD at hospital discharge. Patients with POCD at hospital discharge were more likely to die in the first 3 months after surgery (P 0.02). Likewise, patients who had POCD at both hospital discharge and 3 months after surgery were more likely to die in the first year after surgery (P 0.02). Conclusions: Cognitive dysfunction is common in adult patients of all ages at hospital discharge after major noncardiac surgery, but only the elderly (aged 60 yr or older) are at significant risk for long-term cognitive problems. Patients with POCD are at an increased risk of death in the first year after surgery. POSTOPERATIVE cognitive dysfunction (POCD) is often associated with cardiac surgery, but less is known about the prevalence of this problem after other types of surgery. 1,2 In 1998, the International Study of Postoperative Cognitive Dysfunction (ISPOCD1) evaluated cognitive decline in 1,218 elderly patients, aged 60 yr or older, who had undergone major noncardiac surgery, and found that cognitive dysfunction was present in 26% of older patients 1 week after surgery and in 10% 3 months after surgery. 3 However, this study had significant differences in the incidence of early POCD at the 13 participating hospitals, placing this finding in question. Research evaluating cognitive decline after cardiac and noncardiac surgery has primarily focused on older patients, who might have an increased vulnerability to neurologic deterioration. 1,3,4 However, the cognitive effects of surgery and anesthesia in younger adults are poorly understood, making it difficult to determine whether advancing age is the primary risk factor for this complication. Studies on normal aging have shown that abrupt declines in cognitive function in older adults are associated with early death. 5,6 The relation between POCD and mortality has not been reported. To investigate the hypothesis that advancing age is a risk factor for POCD, we designed a prospective cohort study evaluating the incidence of early (hospital discharge) and late (3 months after surgery) cognitive dysfunction in adults of all ages undergoing elective, major noncardiac surgery. This study used the same neuropsychological methodology as the ISPOCD1 study in an attempt to replicate its results at a single institution. 3 Patients were also followed to determine the impact of POCD on survival in the first year after major surgery. A companion article analyzes the type and severity of cognitive impairment in the elderly patients in this study. 7

https://www.medpagetoday.com/upload/2007/12/27/00000542-200801000-00007.pdf

Predictors of Cognitive Dysfunction after Major Noncardiac Surgery

Because hemiinattention is most commonly caused by right parietal lesions, it is possible that the left hemisphere attends to contralateral stimuli whereas the right attends to both contralateral and ipsilateral stimuli. We gave lateralized visual stimuli to 12 normal subjects and recorded the electroencephalograms. Desynchronization was determined by comparing the alpha power 1 second before and 1 second after a lateralized visual stimulus. Although the left parietal lobe desynchronized most after right-sided stimuli, the right parietal lobe desynchronized equally after right or left stimuli. These findings support the hypothesis that the right hemisphere is dominant for attention.

Kenneth M. Heilman

Papers

Neglect and related disorders

Predictors of Cognitive Dysfunction after Major Noncardiac Surgery

Right hemisphere dominance for attention The mechanism underlying hemispheric asymmetries of inattention (neglect)

Pseudoneglect: effects of hemispace on a tactile line bisection task.

Neglect and related disorders