Deficits in feature-based control of attention in a patient with a right fronto-temporal lesion

Three experiments examined feature-based top-down control of search in a patient with right frontal-temporal lobe brain damage (YW), in comparison with normal control participants. In Experiment 1, YW showed normal search functions for single-feature targets. However, he showed abnormal search functions relative to normal control participants when a singleton distractor irrelevant to the target-defining feature was presented. YW showed longer RTs when a target was presented in the contralesional visual field and a singleton distractor was in the ipsilesional visual field (Experiment 1), or when both were presented in the contralesional visual field (Experiment 2). These results suggest that YW's difficulty is due to a failure of selectivity for targets based on top-down control of target-defining features. Experiment 3 compared singleton detection tasks and feature detection tasks. YW showed no deficits on the singleton detection tasks, where no knowledge of target-defining features was required. However, on the feature detection tasks, YW showed long RTs when targets were presented in the contralesional visual field where knowledge of target-defining features was required. We concluded that YW's difficulty in visual search with singleton distractors was due to deficits in feature-based control. We discuss the role of fronto-temporal regions in feature-based control of attention.     

Impairments of oculomotor control in a patient with a right temporo-parietal lesion

Goal-driven control over saccade target selection requires the inhibition of task-irrelevant, stimulus-driven saccades. A widely held assumption is that frontal structures are of critical importance for this function. Here we report the oculomotor capture behaviour of a patient with a right temporo-parietal lesion, which challenges this view. T.H. was asked to search for a target among distractors and to signal its location with a saccade. A task-irrelevant, additional distractor appeared with or without abrupt onset, and it was either similar or dissimilar in its colour to the target. Compared to controls, T.H. showed an elevated level of capture overall. He also showed spatial extinction, which was partially overridden by an abrupt onset distractor. These results support the view that effective oculomotor control depends on an intact network of frontal and posterior brain regions. We argue that stimulus-driven and goal-driven signals are computed at different stages, but are ultimately combined in a common functional salience map.     

Impairments of oculomotor control in a patient with a right temporo-parietal lesion

Goal-driven control over saccade target selection requires the inhibition of task-irrelevant, stimulus-driven saccades. A widely held assumption is that frontal structures are of critical importance for this function. Here we report the oculomotor capture behaviour of a patient with a right temporo-parietal lesion, which challenges this view. T.H. was asked to search for a target among distractors and to signal its location with a saccade. A task-irrelevant, additional distractor appeared with or without abrupt onset, and it was either similar or dissimilar in its colour to the target. Compared to controls, T.H. showed an elevated level of capture overall. He also showed spatial extinction, which was partially overridden by an abrupt onset distractor. These results support the view that effective oculomotor control depends on an intact network of frontal and posterior brain regions. We argue that stimulus-driven and goal-driven signals are computed at different stages, but are ultimately combined in a common functional salience map.     

Global effects of feature-based attention in human visual cortex

The content of visual experience depends on how selective attention is distributed in the visual field. We used functional magnetic resonance imaging (fMRI) in humans to test whether feature-based attention can globally influence visual cortical responses to stimuli outside the attended location. Attention to a stimulus feature (color or direction of motion) increased the response of cortical visual areas to a spatially distant, ignored stimulus that shared the same feature.     

The spotlight of attention illuminates failed feature-based expectancies

A well-replicated finding is that visual stimuli presented at an attended location are afforded a processing benefit in the form of speeded reaction times and increased accuracy (Mangun, ; Posner,). This effect has been described using a spotlight metaphor, in which all stimuli within the focus of spatial attention receive facilitated processing, irrespective of other stimulus parameters. However, the spotlight metaphor has been brought into question by a series of combined expectancy studies that demonstrated that the behavioral benefits of spatial attention are contingent on secondary feature-based expectancies (Kingstone,). The present work used an event-related potential (ERP) approach to reveal that the early neural signature of the spotlight of spatial attention is not sensitive to the validity of secondary feature-based expectancies.     

An ischemic skin lesion after chemoembolization of the right internal mammary artery in a patient with hepatocellular carcinoma

A huge nodular hepatocellular carcinoma located at the anterior superior portion of the left lobe in a patient with hepatocellular carcinoma was treated with transcatheter arterial chemoembolization through the left hepatic artery. Three months later, however, there was a re-elevation of the serum alpha-fetoprotein level and evidence of a marginal recurrence at the left side of the previously embolized tumor was noted on the postembolization computed tomographic scan. Although the hepatic artery was intact in the second hepatic arteriography, we found that the right internal mammary artery was feeding the recurred hepatocellular carcinoma. This internal mammary artery was successfully treated with Lipiodol-transcatheter arterial chemoembolization. However, an ischemic lesion occurred in the skin of the anterior chest and abdominal wall several days after internal mammary artery embolization. We report here a very rare case of ischemic skin lesion on the anterior chest and abdominal wall following transcatheter arterial chemoembolization of the right internal mammary artery. This internal mammary artery was embolized because it had developed a collateral tumor feeding vessel following the initial chemoembolization of a hepatocellular carcinoma.     

Electrophysiological evidence of feature-based inhibition of focused attention across consecutive trials

Monitoring the visual environment for targets has evolutionary and ecological significance. Exploration of the visual scene can be hypothesized to use "saliency maps" representing the priorities allocated to different locations and features, which change dynamically based on previous experience. This is supported by the observation that sequential effects influence the speed and accuracy of visual search tasks. Yet, the mechanisms underlying these effects are not well understood. Here we used electrophysiological methods to identify some of the mechanisms underlying a specific sequential effect—the distractor previewing effect (DPE). We found that the DPE is correlated with electrophysiological indices of attention allocation but not with sensory or motor components, suggesting that the DPE is related to attentional phenomena, rather than perceptual or motor levels of processing.     

The contribution of stimulus-driven and goal-driven mechanisms to feature-based selection in patients with spatial attention deficits

When people search a display for a target defined by a unique feature, fast saccades are predominantly stimulus-driven whereas slower saccades are primarily goal-driven. Here we use this dissociative pattern to assess whether feature-based selection in patients with lateralized spatial attention deficits is impaired in stimulus-driven processing, goal-driven processing, or both. A group of patients suffering from extinction or neglect after parietal damage, and a group of healthy, age-matched controls, were instructed to make a saccade to a uniquely oriented target line which was presented simultaneously with a differently oriented distractor line. We systematically varied the salience of the target and distractor by changing the orientation of background elements, and used a time-based model to extract stimulus-driven (salience) and goal-driven (target set) components of selection. The results show that the patients exhibited reduced stimulus-driven processing only in the contralesional hemifield, while goal-driven processing was reduced across both hemifields.     

Deficits in involuntary attention switching in obstructive sleep apnea syndrome

Cognitive functions are altered in patients with obstructive sleep apnea syndrome (OSAS) and it has been proposed that vigilance and attentional deficits play a pivotal role in all aspects of these deficits. One way to assess attentional system integrity is the study of event-related-potentials (ERP), but only a few ERP studies have been conducted in patients with OSAS. The aim of the study was to use ERP to further assess attentional impairments in these patients. Thirteen OSAS patients and 13 age-matched controls underwent a night of polysomnographic recording. Each subject was also tested with an ERP paradigm where standard (95%, 1000Hz), high deviant (2.5%, 1250Hz) and low deviant (2.5%, 1050Hz) tones were presented. Subjects were asked to ignore the stimuli and read during the task. Mismatch negativity (MMN) and P3a amplitudes and latencies were measured. No between-group difference was observed for sleep stages, except a lower percentage of rapid eye movement (REM) sleep in patients with OSAS (p<0.01). Moreover, the OSAS group showed a higher micro-arousal index and more sleep transitions than the control group (p<0.05). A significant group effect was found for the amplitude of the P3a component (p<0.05) that was lower in patients with OSAS for both high and low deviant tones. No between-group difference was found for the MMN and the P3a latencies. In conclusion, patients with OSAS have specific alterations of the P3a component that reflects involuntary attention switching, but automatic auditory processing assessed by MMN appears to be preserved.     

An 80-year-old man with a ring-enhancing right basal ganglia lesion

Cerebral phaeohyphomycosis is a rare diagnosis that designates a central nervous system (CNS) infection by dematiaceous fungi. These organisms most commonly cause cutaneous infections in humans, but much less commonly, they cause CNS disease with evidence of neurotropism. We describe here the clinical course and post-mortem findings in a fatal case of cerebral phaeohyphomycosis occurring in an 80-year-old man. He had a long and complex past medical history and approximately 7 weeks prior to his death, he presented to an outside institution with imaging findings reported to be consistent with a cerebrovascular accident. He was treated with thrombolytic therapy and sent to a rehabilitation program. Approximately 2 weeks prior to his death, he was transferred to our institution with worsening chronic heart failure symptoms. Imaging after admission showed a ring-enhancing lesion and the differential diagnosis shifted to include a primary neoplasm vs. an abscess. There was a downward clinical course and neurosurgical biopsy was declined secondary to predicted poor outcome. A full autopsy was performed and confirmed the pre-mortem imaging findings of a cerebral abscess with multiple satellite lesions. The histologic and microbiologic findings were characteristic of cerebral phaeohyphomycosis. Microbiological features and disease characteristics of these organisms as well as incidence and populations affected are also discussed.     

The approach to the patient with a difficult melanocytic lesion

Although most histological diagnoses are made with relative ease and with great specificity and reproducibility, there is a subset of cases in which a specific and reproducible diagnosis is difficult or even impossible to render. In the melanocytic system, these cases can be divided into two broad categories. The first category, 'superficial atypical melanocytic proliferations of uncertain significance' (SAMPUS), includes predominantly junctional melanocytic proliferations, and melanocytic proliferations that are confined to the epidermis and papillary dermis, without evidence of tumorigenic proliferation or mitotic activity there. The prognosis for cure of these lesions is excellent if they are completely excised. Such lesions may include, for example, dysplastic naevi, Spitz naevi or pigmented spindle cell naevi with a few atypical melanocytes above the dermal-epidermal junction, or with greater than average cytological atypia, or with mitoses, where the differential diagnosis of melanoma in situ is difficult or impossible to rule out. The other category, 'melanocytic tumours of uncertain malignant potential' (MELTUMP), is comprised of melanocytic proliferations that form tumours in the dermis, and are therefore potentially capable of metastasis. Examples of such lesions may include atypical Spitz naevi, deep penetrating naevi, possible naevoid melanomas, or cellular blue naevi, where because of increased mitotic activity or cytologic atypia, a diagnosis of invasive or tumorigenic melanoma cannot be ruled out. In managing such lesions, we follow two main principles. The first is to manage each lesion with therapy designed to be adequate for management of the most significant consideration in the differential diagnosis. The second principle is to make clinicians and patients specifically aware of the diagnostic difficulty in their lesion, so that management can be undertaken on a true informed consent basis.     

Condyloma acuminatum presenting as a dorsal tongue lesion in a patient with AIDS

Oral lesions have been recognized as a prominent feature of HIV infection and AIDS since the beginning of the epidemic. This report describes the case of a man with advanced AIDS and a nonpainful but enlarging dorsal tongue soft tissue growth of 6 months' duration. Incisional biopsy showed a red, papillary lesion with koilocytosis consistent with condyloma acuminatum. In situ hybridization and molecular techniques were used to identify human papillomavirus (HPV)-31 sequences in warty tissue. Eighteen months later, the lesion recurred and was reexcised without complication. This case is reported to illustrate that venereal transmission may not be as important in warts of the oral cavity as in HIV-associated anogenital warts, because warts of the oral cavity are rarely associated with HPV types 6, 11, 16, and 18. Instead, they may be present as a result of activation of latent HPV infection or perhaps autoinfection from skin and facial lesions. The carcinogenic potential of oral warts in HIV disease is undefined, as is the role of antiretroviral therapy in controlling HPV-associated oral lesions.     

Pathological findings after right lung transplantation in a patient with fibrosing alveolitis

The pathological findings in a patient who died two months after right lung transplantation for fibrosing alveolitis are reported. The cause of death was haemoptysis, due to penetrating ulceration causing a fistula between the surface of the cartilagenous part of the main bronchus of the donor lung and the right upper lobe pulmonary artery. The opening in the donor bronchus was immediately distal to the line of the bronchial anastomosis and through an actively inflamed area. Other parts of the donor bronchus had microscopic changes suggesting ischaemia, emphasizing that inadequacy of blood supply to the donor extrapulmonary bronchus is one of the most serious hazards of lung transplantation. Within the lung, histological features of rejection were mild and there was minimal evidence of infection. Another question raised by this case is whether the donor lung was in the process of developing the original disease, evidence for which was sought electron microscopically but was not proven.     

Anatomic feature-based registration for patient set-up in head and neck cancer radiotherapy

Modern radiotherapy equipment is capable of delivering high precision conformal dose distributions relative to isocentre. One of the barriers to precise treatments is accurate patient re-positioning before each fraction of treatment. At Massachusetts General Hospital, we perform daily patient alignment using radiographs, which are captured by flat panel imaging devices and sent to an analysis program. A trained therapist manually selects anatomically significant features in the skeleton, and couch movement is computed based on the image coordinates of the features. The current procedure takes about 5 to 10 min and significantly affects the efficiency requirement in a busy clinic. This work presents our effort to develop an improved, semi-automatic procedure that uses the manually selected features from the first treatment fraction to automatically locate the same features on the second and subsequent fractions. An implementation of this semi-automatic procedure is currently in clinical use for head and neck tumour sites. Radiographs collected from 510 patient set-ups were used to test this algorithm. A mean difference of 1.5 mm between manual and automatic localization of individual features and a mean difference of 0.8 mm for overall set-up were seen.