We review evidence for partially segregated networks of brain areas that carry out different attentional functions. One system, which includes parts of the intraparietal cortex and superior frontal cortex, is involved in preparing and applying goal-directed (top-down) selection for stimuli and responses. This system is also modulated by the detection of stimuli. The other system, which includes the temporoparietal cortex and inferior frontal cortex, and is largely lateralized to the right hemisphere, is not involved in top-down selection. Instead, this system is specialized for the detection of behaviourally relevant stimuli, particularly when they are salient or unexpected. This ventral frontoparietal network works as a 'circuit breaker' for the dorsal system, directing attention to salient events. Both attentional systems interact during normal vision, and both are disrupted in unilateral spatial neglect.

Control of goal-directed and stimulus-driven attention in the brain

Publisher Summary This chapter focuses on the modern notion of short-term memory, called working memory. Working memory refers to the temporary maintenance of information that was just experienced or just retrieved from long-term memory but no longer exists in the external environment. These internal representations are short-lived, but can be maintained for longer periods of time through active rehearsal strategies, and can be subjected to various operations that manipulate the information in such a way that makes it useful for goal-directed behavior. Working memory is a system that is critically important in cognition and seems necessary in the course of performing many other cognitive functions, such as reasoning, language comprehension, planning, and spatial processing. This chapter demonstrates the functional importance of dopamine to working memory function in several ways. Elucidation of the cognitive and neural mechanisms underlying human working memory is an important focus of cognitive neuroscience and neurology for much of the past decade. One conclusion that arises from research is that working memory, a faculty that enables temporary storage and manipulation of information in the service of behavioral goals, can be viewed as neither a unitary, nor a dedicated system. Data from numerous neuropsychological and neurophysiological studies in animals and humans demonstrates that a network of brain regions, including the prefrontal cortex, is critical for the active maintenance of internal representations.

Chapter 11 Working memory

https://surfer.nmr.mgh.harvard.edu/ftp/articles/desikan06-parcellation.pdf

An automated labeling system for subdividing the human cerebral cortex on MRI scans into gyral based regions of interest.

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

Using functional magnetic resonance imaging (fMRI), we found an area in the fusiform gyrus in 12 of the 15 subjects tested that was significantly more active when the subjects viewed faces than when they viewed assorted common objects. This face activation was used to define a specific region of interest individually for each subject, within which several new tests of face specificity were run. In each of five subjects tested, the predefined candidate “face area” also responded significantly more strongly to passive viewing of (1) intact than scrambled two-tone faces, (2) full front-view face photos than front-view photos of houses, and (in a different set of five subjects) (3) three-quarter-view face photos (with hair concealed) than photos of human hands; it also responded more strongly during (4) a consecutive matching task performed on three-quarter-view faces versus hands. Our technique of running multiple tests applied to the same region defined functionally within individual subjects provides a solution to two common problems in functional imaging: (1) the requirement to correct for multiple statistical comparisons and (2) the inevitable ambiguity in the interpretation of any study in which only two or three conditions are compared. Our data allow us to reject alternative accounts of the function of the fusiform face area (area “FF”) that appeal to visual attention, subordinate-level classification, or general processing of any animate or human forms, demonstrating that this region is selectively involved in the perception of faces.

/pdf/the-fusiform-face-area-a-module-in-human-extrastriate-cortex-2xuspzx096.pdf

The Fusiform Face Area: A Module in Human Extrastriate Cortex Specialized for Face Perception

The ethical conduct of research on posttraumatic stress disorder (PTSD) requires assessing the risks to study participants. Some previous findings suggest that patients with PTSD report higher distress compared to non-PTSD participants after trauma-focused research. However, the impact of study participation on participant risk, such as suicidal/homicidal ideation and increased desire to use drugs or alcohol, has not been adequately investigated. Furthermore, systematic evaluation of distress using pre- and post-study assessments, and the effects of study procedures involving exposure to aversive stimuli, are lacking. Individuals with a history of PTSD ( n =68) and trauma-exposed non-PTSD controls ( n =68) responded to five questions about risk and distress before and after participating in research procedures including a PTSD diagnostic interview and a behavioral task with aversive stimuli consisting of mild electrical shock. The desire to use alcohol or drugs increased modestly with study participation among the subgroup ( n =48) of participants with current PTSD. Participation in these research procedures was not associated with increased distress or participant risk, nor did study participation interact with lifetime PTSD diagnosis. These results suggest some increase in distress with active PTSD but a participant risk profile that supports a favorable risk–benefit ratio for conducting research in individuals with PTSD.

/pdf/acute-effects-of-trauma-focused-research-procedures-on-2yrysjy8po.pdf

Acute effects of trauma-focused research procedures on participant safety and distress

Functional magnetic resonance imaging in a visual oddball task

Medial temporal lobe epilepsy without hippocampal atrophy

Combining ERP and fMRI methods to elucidate the time course and anatomical basis of information processing may provide a powerful new tool for understanding human brain function. Attempts to model the time course of fMRI activations by recording surface electromagnetic fields require a better understanding of the relationship between ERPs and fMRI activations. The results presented here show that good correspondence can be obtained between the location of ERP generators and fMRI activations in sensorimotor cortex, and in face perception and target detection tasks. However, difficulties in obtaining somatosensory fMRI activations with stimuli known to evoke robust SEPs, and the lack of fMRI activations within the hippocampus in tasks that elicit large hippocampal field potentials suggest that not all stimuli or tasks that evoke focal ERPs will evoke fMRI activations. This may be related to differences in the sensitivity of the fMRI that will be overcome with better technique and with more sensitive instruments. However, caution must be exercised in developing models that assume a one-to-one correspondence between ERP generators and fMRI activations.

Event-related potentials and functional MRI: a comparison of localization in sensory, perceptual and cognitive tasks.

We have demonstrated that a time series of echoplanar images can contain low frequency noise components which confound analysis of functional MRI data. In simulated tasks of long duration, the false positive rate from t-test analyses greatly exceeded the statistical probability level. As task durations were shortened, the false positive rate declined. We also demonstrated that voxels representing extensive regions of the brain covary significantly over time. This covariation challenges the independence assumption of t-test and other analytical procedures and likely contributes to the false positive rate. The frequency spectra of many voxels showed relatively little power at higher frequencies with the important exception of some blood vessels (Fig. 12). Experimental designs in which stimulus or task conditions were alternated at these higher frequencies (e.g. 0.083 Hz corresponding to a 6 sec task duration and a 12 sec period for a complete two task cycle) did not show an inflated false positive rate when analyzed by t-test. We used the alternating tasks design with task durations of 8.73 sec, 6.4 sec, and 6.0 sec coupled with a frequency domain analysis strategy in a series of somatosensory, motor, perceptual, and working memory experiments. This combination of design and analysis was successful in identifying reliable activations across groups of subjects with a minimum of apparently spurious activations. By introducing a 180 degrees phase shift by reversing task order, we have been able to eliminate the contribution of most high frequency noise sources (such as large blood vessels). By segregating low frequency noise from the frequency of stimulus alternation, we routinely generate stable results in the presence of low frequency noise and drift. Despite the usefulness of the rapid task alternation and frequency domain techniques demonstrated here, there are potential problems and limitations in their application: 1. The short duration of our tasks results in an approximately sinusoidal activation waveform. With longer duration tasks, the activation time course would appear more square with a more complex frequency spectrum than the single peak demonstrated above. In such circumstances we have used convolution analysis with an expected waveform (McCarthy et al. 1996), similar to the approach of Bandettini et al. (1993). 2. If the activation in one task condition is significantly delayed and extends well into the period of the second task, it will be difficult to determine which task produced the activation. This problem is not specific to frequency analysis, and would occur as well for t-tests. One solution we have used is running a single active task against a relatively neutral control such as fixation to determine the usual activation dynamics of the active task. 3. Common activations by two alternating tasks are de-emphasized. This problem is also not specific to frequency analysis, and in most circumstances is an advantage rather than a disadvantage. However, if uncertain as to whether a task is capable of producing any activation, we have again used the strategy of running the task against a relatively neutral control. 4. Some tasks do not lend themselves to the short durations used here. 5. The frequency domain procedures used are conservative and may underestimate the true anatomical extent of the activation. In practice we compute t-tests in addition to the frequency domain techniques to guard against this possibility. Many of the advantages of the procedures described here are due to the alternation of short duration tasks rather than the application of frequency domain techniques per se. However, the success of these techniques in isolating periodic task-related signal changes suggest that a more complex design with concurrent stimulation presented at different frequencies might be feasible. Such designs may have advantages in that categories of stimuli would not be presented in isolation but against a changing ba

Gregory McCarthy

Papers

Acute effects of trauma-focused research procedures on participant safety and distress

Functional magnetic resonance imaging in a visual oddball task

Medial temporal lobe epilepsy without hippocampal atrophy

Event-related potentials and functional MRI: a comparison of localization in sensory, perceptual and cognitive tasks.

Magnetic resonance imaging studies of functional brain activation: analysis and interpretation.