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PubMed1998

Sensory gain control (amplification) as a mechanism of selective attention: electrophysiological and neuroimaging evidence.

Both physiological and behavioral studies have suggested that stimulus-driven neural activity in the sensory pathways can be modulated in amplitude during selective attention. Recordings of event-related brain potentials indicate that such sensory gain control or amplification processes play an important role in visual-spatial attention. Combined event-related brain potential and neuroimaging experiments provide strong evidence that attentional gain control operates at an early stage of visual processing in extrastriate cortical areas. These data support early selection theories of attention and provide a basis for distinguishing between separate mechanisms of attentional suppression (of unattended inputs) and attentional facilitation (of attended inputs).

Attention↗
PubMed1998

Memory, consciousness and neuroimaging.

Neuroimaging techniques that allow the assessment of memory performance in healthy human volunteers while simultaneously obtaining measurements of brain activity in vivo may offer new information on the neural correlates of particular forms of memory retrieval and their association with consciousness and intention. We consider evidence from studies with positron emission tomography and functional magnetic resonance imaging indicating that priming, a form of implicit retrieval, is associated with decreased activity in various cortical regions. We also consider evidence concerning the question of whether two components of explicit retrieval--intentional or effortful search and successful conscious recollection--are preferentially associated with increased activity in prefrontal and medial temporal regions, respectively. Last, we consider recent efforts to probe the relation between the phenomenological character of remembering and neural activity. In this instance we broaden our scope to include studies employing event-related potentials and consider evidence concerning the neural correlates of qualitatively different forms of memory, including memory that is specifically associated with a sense of self, and the recollection of particular temporal or perceptual features that might contribute to a rich and vivid experience of the past.

Brain↗
PubMed1998

Towards a functional neuroanatomy of conscious perception and its modulation by volition: implications of human auditory neuroimaging studies.

Conscious sensory perception and its modulation by volition are integral to human mental life. Functional neuroimaging techniques provide a direct means of identifying and characterizing in vivo the systems-level patterns of brain activity associated with such mental functions. In a series of positron emission tomography activation experiments, we and our colleagues have examined a range of normal and abnormal auditory states that, when contrasted, provide dissociations relevant to the question of the neural substrates of sensory awareness. These dissociations include sensory awareness in the presence and absence of external sensory stimuli, the transition from sensory unawareness to awareness (or vice versa) in the presence of sensory stimuli, and sensory awareness with and without volition. The auditory states studied include hallucinations, mental imagery, cortical deafness modulated by attention, and hearing modulated by sedation. The results of these studies highlight the distributed nature of the functional neuroanatomy that is sufficient, if not necessary, for sensory awareness. The probable roles of unimodal association (as compared with primary) cortices, heteromodal cortices, limbic/paralimbic regions and subcortical structures (such as the thalamus) are discussed. In addition, interactions between pre- and post-rolandic regions are examined in the context of top-down, volitional modulation of sensory awareness.

Auditory Perception↗
PubMed1999

Statistical limitations in functional neuroimaging. I. Non-inferential methods and statistical models.

Functional neuroimaging (FNI) provides experimental access to the intact living brain making it possible to study higher cognitive functions in humans. In this review and in a companion paper in this issue, we discuss some common methods used to analyse FNI data. The emphasis in both papers is on assumptions and limitations of the methods reviewed. There are several methods available to analyse FNI data indicating that none is optimal for all purposes. In order to make optimal use of the methods available it is important to know the limits of applicability. For the interpretation of FNI results it is also important to take into account the assumptions, approximations and inherent limitations of the methods used. This paper gives a brief overview over some non-inferential descriptive methods and common statistical models used in FNI. Issues relating to the complex problem of model selection are discussed. In general, proper model selection is a necessary prerequisite for the validity of the subsequent statistical inference. The non-inferential section describes methods that, combined with inspection of parameter estimates and other simple measures, can aid in the process of model selection and verification of assumptions. The section on statistical models covers approaches to global normalization and some aspects of univariate, multivariate, and Bayesian models. Finally, approaches to functional connectivity and effective connectivity are discussed. In the companion paper we review issues related to signal detection and statistical inference.

Bayes Theorem↗
PubMed1999

Statistical limitations in functional neuroimaging. II. Signal detection and statistical inference.

The field of functional neuroimaging (FNI) methodology has developed into a mature but evolving area of knowledge and its applications have been extensive. A general problem in the analysis of FNI data is finding a signal embedded in noise. This is sometimes called signal detection. Signal detection theory focuses in general on issues relating to the optimization of conditions for separating the signal from noise. When methods from probability theory and mathematical statistics are directly applied in this procedure it is also called statistical inference. In this paper we briefly discuss some aspects of signal detection theory relevant to FNI and, in addition, some common approaches to statistical inference used in FNI. Low-pass filtering in relation to functional-anatomical variability and some effects of filtering on signal detection of interest to FNI are discussed. Also, some general aspects of hypothesis testing and statistical inference are discussed. This includes the need for characterizing the signal in data when the null hypothesis is rejected, the problem of multiple comparisons that is central to FNI data analysis, omnibus tests and some issues related to statistical power in the context of FNI. In turn, random field, scale space, non-parametric and Monte Carlo approaches are reviewed, representing the most common approaches to statistical inference used in FNI. Complementary to these issues an overview and discussion of non-inferential descriptive methods, common statistical models and the problem of model selection is given in a companion paper. In general, model selection is an important prelude to subsequent statistical inference. The emphasis in both papers is on the assumptions and inherent limitations of the methods presented. Most of the methods described here generally serve their purposes well when the inherent assumptions and limitations are taken into account. Significant differences in results between different methods are most apparent in extreme parameter ranges, for example at low effective degrees of freedom or at small spatial autocorrelation. In such situations or in situations when assumptions and approximations are seriously violated it is of central importance to choose the most suitable method in order to obtain valid results.

Biometry↗
PubMed1999

When encoding yields remembering: insights from event-related neuroimaging.

To understand human memory, it is important to determine why some experiences are remembered whereas others are forgotten. Until recently, insights into the neural bases of human memory encoding, the processes by which information is transformed into an enduring memory trace, have primarily been derived from neuropsychological studies of humans with select brain lesions. The advent of functional neuroimaging methods, such as positron emission tomography (PET) and functional magnetic resonance imaging (fMRI), has provided a new opportunity to gain additional understanding of how the brain supports memory formation. Importantly, the recent development of event-related fMRI methods now allows for examination of trial-by-trial differences in neural activity during encoding and of the consequences of these differences for later remembering. In this review, we consider the contributions of PET and fMRI studies to the understanding of memory encoding, placing a particular emphasis on recent event-related fMRI studies of the Dm effect: that is, differences in neural activity during encoding that are related to differences in subsequent memory. We then turn our attention to the rich literature on the Dm effect that has emerged from studies using event-related potentials (ERPs). It is hoped that the integration of findings from ERP studies, which offer higher temporal resolution, with those from event-related fMRI studies, which offer higher spatial resolution, will shed new light on when and why encoding yields subsequent remembering.

Brain↗
PubMed2001

The Functional Magnetic Resonance Imaging Data Center (fMRIDC): the challenges and rewards of large-scale databasing of neuroimaging studies.

The Functional Magnetic Resonance Imaging Data Center (fMRIDC) (http://www.fmridc.org) was established in the Autumn of 1999 with the objective of creating a mechanism by which members of the neuroscientific community may more easily share functional neuroimaging data. Examples in other sciences offer proof of the usefulness and benefit that sharing data provides through encouraging growth and development in those fields. By building a publicly accessible repository of raw data from peer-reviewed studies, the Data Center hopes to create a similarly successful environment for the neurosciences. In this article, we discuss the continuum of data-sharing efforts and provide an overview of the scientific and practical difficulties inherent in managing various fMRI data-sharing approaches. Next, we detail the organization, design and foundation of the fMRIDC, ranging from its current capabilities to the issues involved in the submitting and requesting of data. We discuss how a publicly accessible database enables other fields to develop relevant tools that can aid in the growth of understanding of cognitive processes. Information retrieval and meta-analytic techniques can be used to search, sort and categorize study information with a view towards subjecting study data to secondary 'meta-' and 'mega-analyses'. In addition, we detail the technical and policy challenges that have had to be addressed in the formation of the Data Center. Among others, these include: human subject confidentiality issues; ensuring investigator's rights; heterogeneous data description and organization; development of search tools; and data transfer issues. We conclude with comments concerning the future of the fMRIDC effort, its role in promoting the sharing of neuroscientific data, and how this may alter the manner in which studies are published.

Brain↗
PubMed2002

The neural basis of episodic memory: evidence from functional neuroimaging.

We review some of our recent research using functional neuroimaging to investigate neural activity supporting the encoding and retrieval of episodic memories, that is, memories for unique events. Findings from studies of encoding indicate that, at the cortical level, the regions responsible for the effective encoding of a stimulus event as an episodic memory include some of the regions that are also engaged to process the event 'online'. Thus, it appears that there is no single cortical site or circuit responsible for episodic encoding. The results of retrieval studies indicate that successful recollection of episodic information is associated with activation of lateral parietal cortex, along with more variable patterns of activity in dorsolateral and anterior prefrontal cortex. Whereas parietal regions may play a part in the representation of retrieved information, prefrontal areas appear to support processes that act on the products of retrieval to align behaviour with the demands of the retrieval task.

Brain Mapping↗
PubMed2004

A cognitive neurobiological account of deception: evidence from functional neuroimaging.

An organism may use misinformation, knowingly (through deception) or unknowingly (as in the case of camouflage), to gain advantage in a competitive environment. From an evolutionary perspective, greater tactical deception occurs among primates closer to humans, with larger neocortices. In humans, the onset of deceptive behaviours in childhood exhibits a developmental trajectory, which may be regarded as 'normal' in the majority and deficient among a minority with certain neurodevelopmental disorders (e.g. autism). In the human adult, deception and lying exhibit features consistent with their use of 'higher' or 'executive' brain systems. Accurate detection of deception in humans may be of particular importance in forensic practice, while an understanding of its cognitive neurobiology may have implications for models of 'theory of mind' and social cognition, and societal notions of responsibility, guilt and mitigation. In recent years, functional neuroimaging techniques (especially functional magnetic resonance imaging) have been used to study deception. Though few in number, and using very different experimental protocols, studies published in the peer-reviewed literature exhibit certain consistencies. Attempted deception is associated with activation of executive brain regions (particularly prefrontal and anterior cingulate cortices), while truthful responding has not been shown to be associated with any areas of increased activation (relative to deception). Hence, truthful responding may comprise a relative 'baseline' in human cognition and communication. The subject who lies may necessarily engage 'higher' brain centres, consistent with a purpose or intention (to deceive). While the principle of executive control during deception remains plausible, its precise anatomy awaits elucidation.

Brain↗
PubMed2001

Functional neuroimaging of cognition: state-of-the-art.

This paper presents a brief overview of functional neuroimaging studies of cognitive processes. A "publication profile" is identified for PET and fMRI studies of cognitive functions. It is shown that the number of publications has increased exponentially over the last ten years, and that a set of ten journals accounts for the vast majority of publications. It is argued that the field has moved from a state of explorative character to a state of high theoretical sophistication. With special reference to the contributions in this issue of Scandinavian Journal of Psychology, methodological, topical, regional, and clinical implications of cognitive neuroscientific studies are discussed.

Brain↗
PubMed2001

The role of spatial configuration in tests of working memory explored with functional neuroimaging.

While the importance of the prefrontal cortex for "higher-order" cognitive functions is largely undisputed, no consensus has been reached regarding the fractionation of functions within this region. Several recent functional neuroimaging studies have suggested that the mid-ventrolateral frontal cortex may play an important role in various aspects of human memory. Thus, similar patterns of activation have been observed in this region during analogous spatial, verbal and visual span tasks. In the present study, however, activation was observed in a more dorsolateral region of the lateral frontal cortex during a modified version of the spatial span task, which differed only in the spatial configuration of the array employed. The results of a supplementary behavioral study, designed to investigate this effect further, suggest that in spatial memory tasks certain stimulus configurations may encourage subjects to adopt mnemonic strategies, which may depend upon dorsolateral, rather than ventrolateral, regions of the frontal cortex. These findings shed further light on the functional relationship between dorsal and ventral regions of the lateral frontal cortex and, more specifically, how the "executive" processes assumed to be dependent upon these regions might contribute to aspects of human memory.

Adult↗
PubMed2001

Neuroimaging of declarative memory in schizophrenia.

The past three decades have seen tremendous growth in our understanding of the cerebral underpinnings of schizophrenia. including the neural correlates of the cognitive impairment seen in this syndrome. In this article we review the role that structural and functional neuroimaging has played in elucidating the cerebral basis for the declarative memory deficits associated with schizophrenia. Memory impairment in schizophrenia appears to involve abnormal connectivity between the prefrontal cortex and three regions important in normal learning and memory: the hippocampus, thalamus, and cerebellum.

Cerebellum↗
PubMed2001

Cognitive neuroscience of aging: contributions of functional neuroimaging.

By revealing how brain activity during cognitive performance changes as a function of aging, studies using positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) are contributing to the development of a new discipline of Cognitive Neuroscience of Aging. This article reviews functional neuroimaging studies of cognitive aging in the domains of visual perception, episodic memory encoding and semantic memory retrieval, episodic memory retrieval, implicit memory, and working memory. The most consistent finding of these studies was that brain activity tends to be less lateralized in older adults than in younger adults. This finding is conceptualized in terms of a model called Hemispheric Asymmetry Reduction in Old Adults (HAROLD). According to a compensation hypothesis, bihemispheric involvement could help counteract age-related neurocognitive decline, whereas, according to a dedifferentiation hypothesis, it reflects a difficulty in recruiting specialized neural mechanisms.

Aged↗
PubMed2004

On the role of general system theory for functional neuroimaging.

One of the most important goals of neuroscience is to establish precise structure-function relationships in the brain. Since the 19th century, a major scientific endeavour has been to associate structurally distinct cortical regions with specific cognitive functions. This was traditionally accomplished by correlating microstructurally defined areas with lesion sites found in patients with specific neuropsychological symptoms. Modern neuroimaging techniques with high spatial resolution have promised an alternative approach, enabling non-invasive measurements of regionally specific changes of brain activity that are correlated with certain components of a cognitive process. Reviewing classic approaches towards brain structure-function relationships that are based on correlational approaches, this article argues that these approaches are not sufficient to provide an understanding of the operational principles of a dynamic system such as the brain but must be complemented by models based on general system theory. These models reflect the connectional structure of the system under investigation and emphasize context-dependent couplings between the system elements in terms of effective connectivity. The usefulness of system models whose parameters are fitted to measured functional imaging data for testing hypotheses about structure-function relationships in the brain and their potential for clinical applications is demonstrated by several empirical examples.

Brain↗
PubMed2004

Role of early EEG and neuroimaging in determination of prognosis in children with complex febrile seizure.

BACKGROUND: The present study investigates the role of early use of EEG in children with no known neuropathology prior to the first CFS, and the contribution made by computed tomography (CT) and magnetic resonance imaging (MRI) to treatment and prognosis. METHODS: Over a period of 7 years, the authors evaluated 159 children (age range: 2 months-5 years) who were being treated for CFS at Haydarpasa Numune Training and Research Hospital, Pediatrics Clinic, Istanbul, Turkey, and who had no previously known neurological disorder. Patients who presented with febrile seizure were determined to have CFS if they fulfilled the following criteria: <3 months of age when seizure occurred, duration of seizure >/=15 min, more than one seizure occurred during a single episode of illness, or focal seizures and postictal neurological deficit was found. EEG was performed on all patients. CT was performed on the patients who had postictal neurologic deficit or focal seizures. Cranial MRI was performed on patients who had focal findings in their EEGs. RESULTS: Electroencephalogram abnormality was found in 71 cases; 51 of these were diagnosed with epilepsy during follow up. Six of the 16 cases whose EEGs were abnormal between days 2 and 6 were diagnosed with epilepsy. Twenty of the 30 cases whose EEGs were abnormal between days 7 and 10 were diagnosed with epilepsy. All 25 cases who had abnormal EEGs after day 11 were diagnosed with epilepsy. CT was performed for 36 patients, of which five were found to have pathological changes. Pathological changes were detected in two of the nine patients who had cranial MRI. Patients who received CT or MRI were all diagnosed with epilepsy during follow up. CONCLUSION: The results suggest that if neurological examination of CFS patients are normal after their clinical status has stabilised, EEG should be performed after 7 days at the earliest, however for the most accurate diagnosis EEG should be performed 10 days after CFS. The most important predictor for neuroimaging was found to be detection of postictal neurologic deficit. MRI had no advantages over CT in first treating CFS in the emergency unit.

Age Factors↗
PubMed2004

Addiction, a condition of compulsive behaviour? Neuroimaging and neuropsychological evidence of inhibitory dysregulation.

AIMS: Addiction has been conceptualized as a shift from controlled experimentation to uncontrolled, compulsive patterns of use. Current neurobiological models of addiction emphasize changes within the brain's reward system, such that drugs of abuse 'hijack' this system and bias behaviour towards further drug use. While this model explains the involuntary nature of craving and the motivational drive to continue drug use, it does not explain fully why some addicted individuals are unable to control their drug use when faced with potentially disastrous consequences. In this review, we argue that such maladaptive and uncontrolled behaviour is underpinned by a failure of the brain's inhibitory control mechanisms. DESIGN: Relevant neuroimaging, neuropsychological and clinical studies are reviewed, along with data from our own research. FINDINGS: The current literature suggests that in addition to the brain's reward system, two frontal cortical regions (anterior cingulate and orbitofrontal cortices), critical in inhibitory control over reward-related behaviour, are dysfunctional in addicted individuals. These same regions have been implicated in other compulsive conditions characterized by deficits in inhibitory control over maladaptive behaviours, such as obsessive-compulsive disorder. CONCLUSIONS: We propose that in chronically addicted individuals, maladaptive behaviours and high relapse rates may be better conceptualized as being 'compulsive' in nature as a result of dysfunction within inhibitory brain circuitry, particularly during symptomatic states. This model may help to explain why some addicts lose control over their drug use, and engage in repetitive self-destructive patterns of drug-seeking and drug-taking that takes place at the expense of other important activities. This model may also have clinical utility, as it allows for the adoption of treatments effective in other disorders of inhibitory dysregulation.

Behavior, Addictive↗
PubMed2005

Neuroimaging the serial position curve. A test of single-store versus dual-store models.

Neuroimaging data could help clarify the long-standing dispute between dual-store and single-store models of the serial position curve. Dual-store models assume that retrieval from late positions is dependent on short-term memory (STM), whereas retrieval from early positions is dependent on long-term memory (LTM). Single-store models, however, assume that retrieval processes for early and late items are similar, but that early items are more difficult to discriminate than late items. The present study used functional magnetic resonance imaging to examine this question. Ten young adults were scanned while they recognized items from early or late serial positions. Recognition of early items uniquely activated brain areas traditionally associated with LTM, namely, regions within the hippocampal memory system. None of these areas was activated for retrieval of late items. These results indicate differential use of LTM retrieval processes, and therefore support dual-store models over single-store models.

Adult↗
PubMed2004

Neurophysiological tests and neuroimaging procedures in non-acute headache: guidelines and recommendations.

The use of instrumental examinations in headache patients varies widely. In order to evaluate their usefulness, the most common instrumental procedures were evaluated, on the basis of evidence from the literature, by an EFNS Task Force (TF) on neurophysiological tests and imaging procedures in non-acute headache patients. The conclusions of the TF regarding each technique are expressed in the following guidelines for clinical use. 1 Interictal electroencephalography (EEG) is not routinely indicated in the diagnostic evaluation of headache patients. Interictal EEG is, however, indicated if the clinical history suggests a possible diagnosis of epilepsy (differential diagnosis). Ictal EEG could be useful in certain patients suffering from hemiplegic and basilar migraine. 2 Recording of evoked potentials is not recommended for the diagnosis of headache disorders. 3 There is no evidence to justify the recommendation of autonomic tests for the routine clinical examination of headache patients. 4 Manual palpation of pericranial muscles, with standardized palpation pressure, can be recommended for subdividing patient groups but not for diagnosis. Pressure algometry and electromyography (EMG) cannot be recommended as clinical diagnostic tests. 5 In adult and paediatric patients with migraine, with no recent change in attack pattern, no history of seizures, and no other focal neurological signs or symptoms, the routine use of neuroimaging is not warranted. In patients with atypical headache patterns, a history of seizures and/or focal neurological signs or symptoms, magnetic resonance imaging (MRI) may be indicated. 6 If attacks can be fully accounted for by the standard headache classification [International Headache Society (IHS)], a positron emission tomography (PET) or single-photon emission computerized tomography (SPECT) and scan will generally be of no further diagnostic value. 7 Nuclear medicine examinations of the cerebral circulation and metabolism can be carried out in subgroups of headache patients for diagnosis and evaluation of complications, when patients experience unusually severe attacks, or when the quality or severity of attacks has changed. 8 Transcranial Doppler examination is not helpful in headache diagnosis. Although many of the examinations described are of little or no value in the clinical setting, most of the tools have a vast potential for further exploring the pathophysiology of headaches and the effects of pharmacological treatment.

Diagnosis, Differential↗