Search PubMed⌕ Search

Biomedical subjects

Martha J Farah

Publications and source records attributed to Martha J Farah.

At least 19 recordsLinked to original sources
PubMed2006

Memories affect mood: evidence from covert experimental assignment to positive, neutral, and negative memory recall.

Memory recall has been proposed as a common and effective mood regulation strategy. Although several studies have presented results suggesting that recalling valenced memories affects subsequent mood, their designs allow for alternative interpretations of the observed effects. Two such alternatives include the reverse effect (mood effects on memory due to non-experimental assignment to memory recall condition) and demand characteristics of the experiment. We used covert experimental assignment to memory condition, asking subjects (N=314; 56% female) to recall memories that were primarily positive, neutral, or negative. Results showed the expected effect on mood (p<.002), with reported mood worst in the negative memory condition, better in the neutral condition, and best in the positive condition. These results suggest that valenced memory recall does indeed exert an effect on mood, and may do so even without the individual's awareness.

Adaptation, Psychological↗
PubMed2006

Childhood poverty: specific associations with neurocognitive development.

Growing up in poverty is associated with reduced cognitive achievement as measured by standardized intelligence tests, but little is known about the underlying neurocognitive systems responsible for this effect. We administered a battery of tasks designed to tax-specific neurocognitive systems to healthy low and middle SES children screened for medical history and matched for age, gender and ethnicity. Higher SES was associated with better performance on the tasks, as expected, but the SES disparity was significantly nonuniform across neurocognitive systems. Pronounced differences were found in Left perisylvian/Language and Medial temporal/Memory systems, along with significant differences in Lateral/Prefrontal/Working memory and Anterior cingulate/Cognitive control and smaller, nonsignificant differences in Occipitotemporal/Pattern vision and Parietal/Spatial cognition.

Adolescent↗
PubMed2006

Distinct patterns of viewpoint-dependent BOLD activity during common-object recognition and mental rotation.

A fundamental but unanswered question about the human visual system concerns the way in which misoriented objects are recognized. One hypothesis maintains that representations of incoming stimuli are transformed via parietally based spatial normalization mechanisms (eg mental rotation) to match view-specific representations in long-term memory. Using fMRI, we tested this hypothesis by directly comparing patterns of brain activity evoked during classic mental rotation and misoriented object recognition involving everyday objects. BOLD activity increased systematically with stimulus rotation within the ventral visual stream during object recognition and within the dorsal visual stream during mental rotation. More specifically, viewpoint-dependent activity was significantly greater in the right superior parietal lobule during mental rotation than during object recognition. In contrast, viewpoint-dependent activity was significantly greater in the right fusiform gyrus during object recognition than during mental rotation. In addition to these differences in viewpoint-dependent activity, object recognition and mental rotation produced distinct patterns of brain activity, independent of stimulus rotation: object recognition resulted in greater overall activity within ventral stream visual areas and mental rotation resulted in greater overall activity within dorsal stream visual areas. The present results are inconsistent with the hypothesis that misoriented object recognition is mediated by structures within the parietal lobe that are known to be involved in mental rotation.

Adolescent↗
PubMed2006

Brain-behavior relationships in reading acquisition are modulated by socioeconomic factors.

Functional neuroimaging may provide insights into the achievement gap in reading skill commonly observed across socioeconomic status (SES). Brain activation during reading tasks is known to be associated with individual differences in children's phonological language skills. By selecting children of equivalent phonological skill, yet diverse socioeconomic backgrounds, we use functional magnetic resonance imaging (fMRI) to demonstrate that a child's experience, as operationalized by SES, can systematically modulate the relationship between phonological language skills and reading-related brain activity in left fusiform and perisylvian regions. Specifically, at lower socioeconomic levels, individual differences in skill result in large differences in brain activation. In contrast, as SES increases, this relationship between phonological language skill and activation is attenuated. Socioeconomic background factors are thus found to modulate brain-behavior relationships in reading, indicating that cognitive, social, and neurobiological influences on reading development are fundamentally intertwined.

Behavior↗
PubMed2006

COMT genotype influences prefrontal response to emotional distraction.

Early studies of genetic effects on brain activity have been conducted to investigate primarily either the influence of polymorphisms in dopaminergic genes, especially the catechol-O-methyltransferase (COMT) gene, on prefrontal cognitive processes such as working memory, or that of polymorphisms in the serotonin transporter gene on the amygdala response to threatening stimuli. Here, we address genetic influences on the neural systems underlying cognitive-affective interactions. Specifically, we assess the effect of the CO MT val158met polymorphism onfrontal regulation of attentionunder emotional distraction. Healthy volunteers were scanned while performing a house-matching task with affectively negative versus neutral distractors. Effects of val allele load were examined on frontal regions associated with attentional control and emotion regulation, and on parahippocampal regions associated with perception of houses. As we predicted, val load correlated positively with activity in control- and task-related regions during performance under emotional distraction. These findings provide an initial step toward identifying genetic contributions to interindividual variability in recruitment of mechanisms that regulate affective processing.

Adolescent↗
PubMed2005

Is anterior cingulate cortex necessary for cognitive control?

Functional neuroimaging studies in normal humans suggest that dorsal anterior cingulate cortex (dACC) plays an important role in cognitive control. This brain area is reliably activated when tasks require the ongoing adjustment of the allocation of attention. The dACC has come to occupy a central role in theories of attention and cognitive control, which hold that dACC either monitors response conflict, signalling the need for adjustments in cognitive processes, or directly mediates such adjustments. However, functional imaging results cannot establish that a brain area is necessary for a particular cognitive process. This requires evidence from loss-of-function studies. Here we assessed cognitive control in four human subjects with damage to dACC and 12 age- and education-matched control subjects using several measures drawn from the functional imaging literature. All four subjects with dACC damage showed normal adjustments in performance following manipulation of response conflict in both Stroop and go-no go tasks. Furthermore, damage to the dACC did not impair the phenomenon of post-error slowing, nor alter the ability to adjust performance in response to explicit speed or accuracy instructions. Thus, cognitive control, as assessed by four different measures in two different tasks, appears to be intact in these subjects, arguing against a necessary role for dACC in this process.

Adult↗
PubMed2005

Dissociable elements of human foresight: a role for the ventromedial frontal lobes in framing the future, but not in discounting future rewards.

Impaired future thinking may be a core aspect of impulsive decision making. Recent efforts to understand the brain processes that underlie impulsivity have suggested a role for the frontal lobes. However, future thinking is unlikely to be a unitary process, and the frontal lobes are not a homogeneous entity. The present study contrasted the effects of dorsolateral and ventromedial frontal lobe damage on two distinct aspects of future thinking in humans. Temporal discounting, the subjective devaluation of reward as a function of delay, is not affected by frontal lobe injury. In contrast, a normal future time perspective (a measure of the length of an individual's self-defined future) depends on the ventromedial, but not dorsolateral, frontal lobes. Furthermore, investigation of the relationship of these two measures with classical symptoms of frontal lobe damage indicates that future time perspective correlates with apathy, not impulsivity. Apathy may deserve more attention in understanding both impaired future thinking and the impaired decision making that may result.

Aged↗
PubMed2005

Neuroethics: the practical and the philosophical.

In comparison with the ethical issues surrounding molecular genetics, there has been little public awareness of the ethical implications of neuroscience. Yet recent progress in cognitive neuroscience raises a host of ethical issues of at least comparable importance. Some are of a practical nature, concerning the applications of neurotechnology and their likely implications for individuals and society. Others are more philosophical, concerning the way we think about ourselves as persons, moral agents and spiritual beings. This article reviews key examples of each type of issue, including the relevant advances in science and technology and their accompanying social and philosophical problems.

Brain↗
PubMed2005

Is self special? A critical review of evidence from experimental psychology and cognitive neuroscience.

Varied research findings have been taken to support the claim that humans' representation of the self is "special," that is, that it emerges from systems that are physically and functionally distinct from those used for more general purpose cognitive processing. The authors evaluate this claim by reviewing the relevant literatures and addressing the criteria for considering a system special, the various operationalizations of self, and how the studies' findings relate to the conclusions drawn. The authors conclude that many of the claims for the special status of self-related processing are premature given the evidence and that the various self-related research programs do not seem to be illuminating a unitary, common system, despite individuals' subjective experience of a unified self.

Brain↗
PubMed2005

Neurocognitive correlates of socioeconomic status in kindergarten children.

Socioeconomic status (SES) is strongly associated with cognitive ability and achievement during childhood and beyond. Little is known about the developmental relationships between SES and specific brain systems or their associated cognitive functions. In this study we assessed neurocognitive functioning of kindergarteners from different socioeconomic backgrounds, using tasks drawn from the cognitive neuroscience literature in order to determine how childhood SES predicts the normal variance in performance across different neurocognitive systems. Five neurocognitive systems were examined: the occipitotemporal/visual cognition system, the parietal/spatial cognition system, the medial temporal/memory system, the left perisylvian/language system, and the prefrontal/executive system. SES was disproportionately associated with the last two, with low SES children performing worse than middle SES children on most measures of these systems. Relations among language, executive function, SES and specific aspects of early childhood experience were explored, revealing intercorrelations and a seemingly predominant role of individual differences in language ability involved in SES associations with executive function.

Brain↗
PubMed2004

Different underlying impairments in decision-making following ventromedial and dorsolateral frontal lobe damage in humans.

Ventromedial prefrontal cortex (VMF) damage can lead to impaired decision-making. This has been studied most intensively with the Iowa gambling task (IGT), a card game that asks subjects to overcome an initial attraction to high-payoff decks as losses begin to accrue. VMF subjects choose from the high risk decks more often than controls, but the fundamental impairments driving poor performance on this complex task have yet to be established. There is also conflicting evidence regarding the role of the dorsolateral prefrontal cortex (DLF) in this task. The present study examined whether poor performance on the IGT was specific for VMF damage and whether fundamental impairments in reversal learning contributed to IGT performance. We found that both VMF and DLF damage leads to impaired IGT performance. The impairment of VMF subjects, but not of DLF subjects, seems to be largely explained by an underlying reversal learning deficit.

Decision Making↗
PubMed2004

Selection ability in Alzheimer's disease: investigation of a component of semantic processing.

Selection ability (selecting a response from several competing semantic and/or lexical representations) was tested in 21 participants with Alzheimer's disease (AD) and 28 control participants to help clarify the nature of semantic impairments in AD. Selection demands were manipulated in 3 tasks (lexical fluency, comparison, and verb generation). In each, high-selection conditions required response selection from competing alternatives, whereas low-selection conditions had a reduced need for selection. Patients with AD were disproportionately impaired on the high-selection conditions of all tasks, even when this condition was easier. Selection deficits on verb generation were evident only relative to nonspeeded controls. Overall results indicate impaired semantic selection abilities in AD, which may contribute to poor performance on some semantic tasks.

Aged↗
PubMed2004

Neuroethics: a guide for the perplexed.

Like filings to a magnet, issues of all shapes, sizes, and degrees of importance are sticking to the idea of neuroethics. Martha Farah, an early thinker in this new field, proposes that, numerous as they are, the problems actually fall into just three categories. She finds that neuroethics has made a quick start sizing up many practical--and some unique--questions swirling up from brain science, but, she writes, watch for challenges that reach beyond these to the metaphysical. Neuroscience may one day explain in terms of neural tissue virtually all aspects of human cognition and emotion--realms traditionally deemed apart from physical law. Thus, we should also expect neuroethics to grapple with our fundamental distinction between persons and mere "things." If mental processes prove to result from purely physical events, this opens to question our notions of consciousness, spirituality, free will, and moral responsibility.

Behavior↗
PubMed2003

Ventromedial frontal cortex mediates affective shifting in humans: evidence from a reversal learning paradigm.

How do the frontal lobes support behavioural flexibility? One key element is the ability to adjust responses when the reinforcement value of stimuli change. In monkeys, this ability--a form of affective shifting known as reversal learning--depends on orbitofrontal cortex. The present study examines the anatomical bases of reversal learning in humans. Subjects with lesions of the ventromedial prefrontal cortex were compared with a group with dorsolateral frontal lobe damage, as well as with normal controls on a simple reversal learning task. Neither form of frontal damage affected initial stimulus-reinforcement learning; ventromedial frontal damage selectively impaired reversal learning.

Adult↗
PubMed2003

Visual object and face processing in mild-to-moderate Alzheimer's disease: from segmentation to imagination.

Little is known about the fate of higher level visual perception and visual mental imagery in the early stages of Alzheimer's disease (AD). In this study, we assessed these abilities in a group of mild-to-moderate AD patients using tasks selected to satisfy two main criteria. First, they have been shown to be sensitive to impairments of perception and imagery caused by other neurological conditions. Second, they test specific stages of visual perception and cognition in a reasonably selective manner. These stages were (in their normal order of occurrence during perception): the segmentation of different local points of the visual field into regions belonging to distinct objects; the representation of the shapes of these segmented regions in the image; the construction of more abstract shape representations that possess constancy over changes in size, location, orientation or illumination (assessed separately for faces and objects); the use of these perceived shape representations to access stored shape representations; and the access of lexical semantic representations from these high-level visual representations. Additional tasks tested the top-down activation of earlier visual representations from the semantic level in visual mental imagery. Our findings indicate small, but in most cases reliable, impairments in visual perception, which are independent of degree of cognitive decline. Deficits in basic shape processing influenced performance on some higher level visual tasks, but did not contribute to poor performance on face processing, or to the profound deficit on object naming. The latter of these is related to semantic-lexical impairment.

Aged↗
PubMed2003

When does the visual system use viewpoint-invariant representations during recognition?

One popular model of object recognition claims that the visual system typically describes objects using view-specific representations, but that viewpoint-invariant representations are used when objects can be specified uniquely by the arrangement of parts along a single dimension. In a series of three naming experiments using novel, two-dimensional line drawings, we test this hypothesis against alternative accounts of when viewpoint-invariant representations are used during the recognition of upright and viewplane-rotated objects. Experiments 1 and 2 demonstrate that the number of dimensions along which featural information must be represented is the only stimulus feature that influences the type of representation used, consistent with the Tarr and Pinker model. Experiment 3, however, reveals that the use of viewpoint-invariant representations during recognition is not driven purely by stimulus features, and is at least partly under voluntary control. These data suggest that viewpoint-invariant representations are not automatically invoked by the visual system when the requisite stimulus features are present. Rather, our results suggest that top-down control processes, as well as bottom-up stimulus features, jointly determine the conditions under which the visual system uses viewpoint-invariant representations during visual recognition.

Functional Laterality↗
PubMed2002

Neural and behavioral substrates of mood and mood regulation.

A review of behavioral and neurobiological data on mood and mood regulation as they pertain to an understanding of mood disorders is presented. Four approaches are considered: 1) behavioral and cognitive; 2) neurobiological; 3) computational; and 4) developmental. Within each of these four sections, we summarize the current status of the field and present our vision for the future, including particular challenges and opportunities. We conclude with a series of specific recommendations for National Institute of Mental Health priorities. Recommendations are presented for the behavioral domain, the neural domain, the domain of behavioral-neural interaction, for training, and for dissemination. It is in the domain of behavioral-neural interaction, in particular, that new research is required that brings together traditions that have developed relatively independently. Training interdisciplinary clinical scientists who meaningfully draw upon both behavioral and neuroscientific literatures and methods is critically required for the realization of these goals.

Affect↗