Our goal in this review is to provide an anatomical framework for the analysis of the motor functions of the medial wall of the hemisphere in humans and laboratory primates. Converging evidence indicates that this region of the frontal robe contains multiple areas involved in motor control. In the monkey, the medial wall contains four premotor areas that project directly to both the primary motor cortex and the spinal cord. These are the supplementary motor area (SMA) on the superior frontal gyrus and three motor areas buried within the cingulate sulcus. In addition, there is evidence that a fifth motor field, the pre-SMA, lies rostral to the SMA proper. Recent physiological observations provide evidence for functional differences among these motor fields. In the human, no consensus exists on the number of distinct motor fields on the medial wall. In this review, we summarize the results of positron emission tomography (PET) studies that examined functional activation on the medial wall of humans. Our analysis suggests that it is possible to identify at least four separate cortical areas on the medial wall. Each area appears to be relatively more involved in some aspects of motor behavior than others. These cortical areas in the human appear to be analogous to the pre-SMA, the SMA proper, and two of the cingulate motor areas of the monkey. We believe that these correspondences and the anatomical framework we describe will be important for unraveling the motor functions of the medial wall of the hemisphere.
This study tested the hypothesis that body mass index (BMI) is representative of body fatness independent of age, sex, and ethnicity, Between 1986 and 1992, the authors studied a total of 202 black and 504 white men and women who resided in or near New York City, were ages 20-94 years, and had BMIs of 18-35 kg/m(2)., Total body fat, expressed as a percentage of body weight (BF%), was assessed using a four-compartment body composition model that does not rely on assumptions known to be age, sex, or ethnicity dependent, Statistically significant age dependencies were observed in the BF%-BMI relations in all four sex and ethnic groups (p values < 0.05-0.001) with older persons showing a higher BF% compared with younger persons with comparable BMIs, Statistically significant sex effects were also observed in BF%-BMI relations within each ethnic group (p values < 0.001) after controlling first for age, For an equivalent BMI, women have significantly greater amounts of total body fat than do men throughout the entire adult life span, Ethnicity did not significantly influence the BF%-BMI relation after controlling first for age and sex even though both black women and men had longer appendicular bone lengths relative to stature (p values < 0.001 and 0.02, respectively) compared with white women and men, Body mass index alone accounted for 25% of between-individual differences in body fat percentage for the 706 total subjects; adding age and sex as independent variables to the regression model increased the variance (r(2)) to 67%. These results suggest that BMI is age and sex dependent when used as an indicator of body fatness, but that it is ethnicity independent in black and white adults.
Brain magnetic resonance images (MRI) of 104 healthy children and adolescents, aged 4-18, showed significant effects of age and gender on brain morphometry. Males had larger cerebral (9%) and cerebellar (8%) volumes (P < 0.0001 and P = 0.008, respectively), which remained significant even after correction for height and weight. After adjusting for cerebral size, the putamen and globus pallidus remained larger in males, while relative caudate size was larger in females. Neither cerebral nor cerebellar volume changed significantly across this age range. Lateral ventricular volume increased significantly in males (trend for females), with males showing an increase in slope after age 11. In males only, caudate and putamen decreased with age (P = 0.007 and 0.05, respectively). The left lateral ventricles and putamen were significantly greater than the right (P = 0.01 and 0.0001, respectively). In contrast, the cerebral hemispheres and caudate showed a highly consistent right-greater-than-left asymmetry (P < 0.0001 for both). All volumes demonstrated a high degree of variability. These findings highlight gender-specific maturational changes of the developing brain and the need for large gender-matched samples in pediatric neuropsychiatric studies.
Following damage to specific sectors of the prefrontal cortex, humans develop a defect in real-life decision making, in spite of otherwise normal intellectual performance. The patients so affected may even realize the consequences of their actions but fail to act accordingly, thus appearing oblivious to the future. The neural basis of this defect has resisted explanation. Here we identify a physiological correlate for the defect and discuss its possible significance. We measured the skin conductance responses (SCRs) of 7 patients with prefrontal damage, and 12 normal controls, during the performance of a novel task, a card game that simulates real-life decision making in the way it factors uncertainty, rewards, and penalties. Both patients and controls generated SCRs after selecting cards that were followed by penalties or by reward. However, after a number of trials, controls also began to generate SCRs prior to their selection of a card, while they pondered from which deck to choose, but no patients showed such anticipatory SCRs. The absence of anticipatory SCRs in patients with prefrontal damage is a correlate of their insensitivity to future outcomes. It is compatible with the idea that these patients fail to activate biasing signals that would serve as value markers in the distinction between choices with good or bad future outcomes; that these signals also participate in the enhancement of attention and working memory relative to representations pertinent to the decision process; and that the signals hail from the bioregulatory machinery that sustains somatic homeostasis and can be expressed in emotion and feeling.
The hippocampus has been proposed as the site of neural representation of large-scale environmental space, based upon the identification of place cells (neurons with receptive fields for current position in the environment) within the rat hippocampus and the demonstration that hippocampal lesions impair place learning in therat. The inability to identify place cells within the monkey hippocampus and the observation that unilateral hippocampal lesions do not selectively impair topographic behavior in humans suggest that alternate regions may subserve this function in man. To examine the contribution of the hippocampus and adjacent medial-temporal lobe structures to topographic learning in the human, a 'virtual' maze was used as a task environment during functional magnetic resonance imaging studies. During the learning and recall of topographic information. medial-temporal activity was confined to the para- hippocampal gyri. This activity accords well with the lesion site known to produce topographical disorientation in humans. Activity was also observed in cortical areas known to project to the parahippocampus and previously proposed to contribute to a network subserving spatially guided behavior.
Three experiments used position emission tomography (PET) to study the neural basis of human working memory, These studies ask whether different neural circuits underly verbal and spatial memory. In Experiment 1, subjects had to retain for 3 sec. either the names of four letters (verbal memory) or the positions of three dots (spatial memory). The PET results manifested a clear cut double dissociation, as the verbal task activated primarily left-hemisphere regions whereas the spatial task activated only right-hemisphere regions, In Experiment 2, the identical sequence of letters was presented in all conditions, and what varied was whether subjects had to remember the names of the letters (verbal memory) or their positions in the display (spatial memory). In the verbal task, activation was concentrated more in the left than the right hemisphere; in the spatial task, there was substantial activation in both hemispheres, though in key regions, there was more activation in the right than the left hemisphere. Experiment 3 studied only verbal memory, and showed that a continuous memory task activated the same regions as the discrete verbal task used in Experiment 1. Taken together, these results indicate that verbal and spatial working memory are implemented by different neural structures.
Human and nonhuman primate visual systems are divided into object and spatial information processing pathways, In the macaque, it has been shown that these pathways project to separate areas in the frontal lobe and that the ventral and dorsal frontal areas are, respectively, involved in working memory for objects and spatial locations. A positron emission tomography (PET) study was done to determine if a similar anatomical segregation exists in humans for object and spatial visual working memory. Face working memory demonstrated significant increases in regional cerebral blood flow (rCBF), relative to location working memory, in fusiform, parahippocampal, inferior frontal, and anterior cingulate cortices, and in right thalamus and midline cerebellum. Location working memory demonstrated significant increases in rCBF relative to face working memory, in superior and inferior parietal cortex, and in the superior frontal sulcus. Our results show that the neural systems involved in working memory for faces and for spatial location are functionally segregated, with different areas recruited in both extrastriate and frontal cortices for processing the two types of visual information.
xIn this prospective study, the authors determined intrinsic risk factors for falls and recurrent falls and constructed a risk profile that indicated the relative contribution of each risk factor and also estimated the probabilities of falls and recurrent falls, In 1992, over a 28-week period, falls were recorded among 354 elderly subjects aged 70 years or over who were living in homes or apartments for the elderly in Amsterdam and the vicinity, During the study period, 251 falls were reported by 126 subjects (36%), and recurrent falls (greater than or equal to 2 falls) were reported by 57 subjects (16%). Associations of falls and recurrent falls with potential risk factors were identified in logistic regression models. Mobility impairment regarding one or more of the tested items (i.e., impairment of balance, leg-extension strength, and gait) was associated with falls (adjusted odds ratio (OR) = 2.6) and was strongly associated with recurrent falls (OR = 5.0). Dizziness upon standing was associated with falls (OR = 2.1) and recurrent falls (OR = 2.1). However, several risk factors were associated with recurrent falls only: history of stroke (OR = 3.4), poor mental state (OR = 2.4), and postural hypotension (OR = 2.0). The authors constructed a risk profile for recurrent falls that included the five risk factors mentioned above. Inclusion of all risk factors in the profile implied an 84% probability of recurrent falls over a period of 28 weeks, compared with 3% when no risk factor was present. The probability of recurrent falls ranged only from 11% to 29% when predicted by number of falls occurring in the previous year. Physical activity, use of high-risk medication, and the use of vitamin D-3, which was randomly allocated to the participants, were not strongly related to either falls or recurrent falls. In conclusion, a large range of probabilities of falls, especially of recurrent falls, was estimated by the risk profiles, in which mobility impairment was the major risk factor. Recurrent fallers may therefore be especially amenable to prevention based on mobility improvement.
In gross anatomical terms, the hippocampal archicortex can be conceived as an ''appendage'' of the large neocortex. In contrast to neocortical areas, the main output targets of the hippocampus are the same as its main inputs (i.e., the entorhinal cortex). Highly processed information about the external world (the content) reaches the hippocampus via the entorhinal cortex, whereas information about the ''internal world'' (the context) is conveyed by the subcortical inputs. Removal of the context makes the content illegible, as demonstrated by the observation that the behavioral impairment following surgical removal of hippocampopetal subcortical inputs is as devastating as removing the hippocampus itself. From its strategic anatomical position and input-output connections, it may be suggested that the main function of the hippocampal formation is to modify its inputs by feeding back a processed ''reafferent copy'' to the neocortex. I hypothesize that neocortico-hippocampal transfer of information and the modification process in neocortical circuitries by the hippocampal output take place in a temporally discontinuous manner and might be delayed by minutes, hours, or days. Acquisition of information may happen very fast during the activated state of the hippocampus associated with theta/gamma oscillations. Intrahippocampal consolidation and the hippocampal-neocortical transfer of the stored representations, on the other hand, is protracted and carried by discrete quanta of cooperative neuronal bursts during slow wave sleep.
Previous work in nonhuman primates and in patients with frontal lobe damage has suggested that the frontal cortex plays a critical role in the performance of both spatial and nonspatial working memory tasks, The present study used positron emission tomography with magnetic resonance imaging to demonstrate the existence, within the human brain, of two functionally distinct subdivisions of the lateral frontal cortex, which may subserve different aspects of spatial working memory, Five spatial memory tasks were used, which varied in terms of the extent to which they required different executive processes. When the task required the organization and execution of a sequence of spatial moves retained in working memory, significant changes in blood flow were observed in ventrolateral frontal cortex (area 47) bilaterally. By contrast, when the task required active monitoring and manipulation of spatial information within working memory, additional activation foci were observed in mid-dorsolateral frontal cortex (areas 46 and 9), These findings support a two-stage model of spatial working memory processing within the lateral frontal cortex.