Variability in blood oxygen level dependent (BOLD) signal in patients with stroke-induced and primary progressive aphasia.

Although fMRI is increasingly used to assess language-related brain activation in patients with aphasia, few studies have examined the hemodynamic response function (HRF) in perilesional, and contralesional areas of the brain. In addition, the relationship between HRF abnormalities and other variables such as lesion size and severity of aphasia has not been explored. The objective of this study was to investigate changes in HRF signal during language-related neural activation in patients with stroke-induced aphasia (SA). We also examined the status of the HRF in patients with aphasia due to nonvascular etiology, namely, primary progressive aphasia (PPA). Five right handed SA patients, three PPA patients, and five healthy individuals participated in the study. Structural damage was quantified with T1-weighted MR images. Functional MR imaging was performed with long trial event-related design and an overt naming task to measure BOLD signal time to peak (TTP) and percent signal change (ΔS). In SA patients, the average HRF TTP was significantly delayed in the left hemisphere regions involved in naming compared to healthy participants and PPA patients. However, ΔS was not different in SA patients compared to the other two groups. Delay in HRF TTP in the left hemisphere naming network of SA patients was correlated with lesion size and showed a negative correlation with global language function. There were no significant differences in the HRF TTP and ΔS in the right hemisphere homologues of the naming network or in the left and the right occipital control regions across the three groups. In PPA patients, HRF had a normal pattern. Our results indicate that abnormal task-related HRF is primarily found in the left hemisphere language network of SA patients and raise the possibility that abnormal physiology superimposed on structural damage may contribute to the clinical deficit. Follow-up investigations in a larger sample of age-matched healthy individuals, SA, and PPA patients will be needed to further confirm and extend our findings.

Loss of spontaneous blinking in a patient with Balint's syndrome.

A patient with Balint's syndrome caused by bilateral parieto-occipital lesions lost spontaneous blinking, suggesting that humans, like nonhuman primates, have parietal lobe neurons that are important for blinking. Although the functions of spontaneous blinking are not known, they may help initiate some saccades and, like saccades, be involved in the cancellation of thalamic inhibitory postsynaptic potentials, thereby facilitating processing of new foveal targets. Spontaneous blinking may also facilitate sensory relay during sustained attention and, therefore, help prevent fading of a retinal image.

Impaired recognition of meaningful sounds in Alzheimer's disease.

We studied recognition of meaningful nonverbal sounds using a sound-picture matching test in 18 patients with senile dementia of the Alzheimer type (SDAT) and 19 age-matched controls. A significant impairment of sound recognition was found in the SDAT group, consistent with auditory sound agnosia. Although sound recognition performance correlated significantly with auditory verbal comprehension scores, a sound recognition defect was also identifiable in the subgroup of patients with SDAT who had normal verbal comprehension. Qualitative analysis of sound recognition errors revealed that nonaphasic patients with SDAT made predominantly acoustic errors, whereas semantic errors were found almost exclusively in aphasic patients. These findings suggest that the auditory sound agnosia of patients with SDAT may be subdivided into perceptual-discriminative and semantic-associative types.

Selective attention in hemispatial neglect.

To determine how increasing demands on visual selective attention affect the symptoms of hemispatial neglect, we studied patients with right hemispheric lesions on a cancellation task requiring various degrees of focused attention. In the target only condition, the patients were to cancel all stimuli. In the target-nontarget condition, discriminating targets from nontargets did not require close scrutiny, whereas in the target-foil condition, discriminating targets from foils required greater attention to detail. Our findings indicate that increasing demands on visual selective attention adversely affect both exploration of the left side of space and visual discrimination.

Lexical agraphia in Alzheimer's disease.

We studied spelling in 11 patients with senile dementia of the Alzheimer type (SDAT), and their performance was contrasted with that of normal controls. A consistent and specific pattern of linguistic agraphia was identified in the group with SDAT. Although patients with SDAT spelled regular words and nonwords as well as controls, they performed significantly worse when they spelled irregular words. These findings indicated an impairment of the lexical spelling system, consistent with the diagnosis of lexical agraphia. Our observations suggested a loss of word representations from the orthographic lexicon in SDAT and/or an inability to access these representations. However, phonological spelling (phoneme-grapheme conversion) was largely spared.

'Peduncular hallucinosis' following paramedian thalamic infarction.

An 83-year-old man had the sudden onset of vivid formed hallucinations, agitation, and sleep disturbance suggesting "peduncular hallucinosis." A magnetic resonance scan revealed a right paramedian thalamic infarction with no abnormality of the cerebral peduncles or midbrain.

Altitudinal neglect.

Previous clinical observations on patients with hemispatial neglect from unilateral hemispheric lesions suggest the brain's attentional mechanisms are organized along the horizontal dimensions of extrapersonal space. We now report a patient with Balint's syndrome caused by bilateral parieto-occipital infarctions, who demonstrated altitudinal neglect. On visual and tactile bisection of vertical rods, the patient consistently placed her mark well above the true midpoint, and this performance remained unchanged when the stimuli were simultaneously explored visually and tactually. She also showed altitudinal inattention in the visual modality by extinguishing the stimulus presented in the lower quadrants during double simultaneous stimulation across the horizontal meridian. These findings suggest that bilateral damage to the parietal lobes can lead to multimodal attentional and exploratory deficits along the vertical dimensions of extrapersonal space.

Lexical agraphia from focal lesion of the left precentral gyrus.

Lexical agraphia reflects a dysfunction of the lexical spelling system and is characterized by better spelling of nonwords and regular words than irregular words. All previously reported cases with documented focal lesions had involvement of temporo-parieto-occipital regions. We now report a case of lexical agraphia following a discrete lesion of the left precentral gyrus. Our case complements previous neuroanatomical accounts of agraphia and provides further support for the independence of neuronal systems that mediate spelling from those involved in spoken language and reading.

Apraxia in Alzheimer's disease.

We studied apraxia in 28 patients with senile dementia of the Alzheimer type (SDAT). Although SDAT patients were impaired compared with age-matched controls on tests of ideomotor and ideational apraxia, not all types of movements were affected to the same degree. Limb transitive movements were especially vulnerable, while limb intransitive, buccofacial, and axial movements were relatively spared. When pantomiming limb transitive movements, SDAT patients made frequent body part as object and spatial errors. There was no significant difference between performance on verbal command and imitation, but there was considerable improvement with the use of actual objects. Disorders of skilled movement in SDAT were qualitatively similar to the apraxic syndromes following left parietal damage. Apraxia in SDAT suggests posterior left hemisphere cortical involvement and may be apparent even in patients with good language functions.

Selective deficit of praxis imagery in ideomotor apraxia.

We studied imagery for learned, skilled movements (praxis imagery) in a patient with severe ideomotor apraxia and intact language abilities. This patient, who made predominantly spatial and movement errors when performing transitive movements demonstrating the use of tools (transitive gestures), was also impaired in her ability to answer imagery questions about joint movement or the spatial position of the hands during action. However, visual object imagery was spared. The finding of parallel praxis production and praxis imagery deficits in this patient suggests that the same representations used for gesture production are also activated during imagery of motor acts. Our findings also suggest that certain aspects of motor imagery may be dissociable from general object imagery.

Dissociation between verbal and autonomic measures of memory following frontal lobe damage.

OBJECTIVE: The objective of this study was to contrast overt verbal versus covert autonomic responses to facial stimuli in a patient with false recognition following frontal lobe damage. BACKGROUND: False recognition has been linked to frontal lobe dysfunction. However, previous studies have relied exclusively on overt measures of memory and have not examined whether or not patients with false recognition continue to demonstrate preserved covert discrimination of familiar and unfamiliar items. METHODS: We recorded skin conductance responses (SCRs) in a patient with frontal lobe damage and in normal control subjects while they performed a familiarity decision task using famous and unfamiliar faces as stimuli. RESULTS: Patient J.S. produced significantly more overt false recognition errors and misidentifications in response to unfamiliar faces than control subjects. However, similar to the control subjects, he showed accurate covert autonomic discrimination of truly familiar faces from unfamiliar ones. Furthermore, SCRs to falsely recognized unfamiliar faces were not significantly different from SCRs generated to unfamiliar faces that J.S. correctly rejected. CONCLUSIONS: Our findings provide further neuropsychological evidence that overt and covert forms of face recognition memory are dissociable. In addition, the failure to detect an autonomic correlate for the false recognition errors and misidentifications in J.S. suggests that these memory distortions were not related to the spurious activation of stored memory representations for specific familiar faces. Instead, these incorrect responses may have been driven by the sense of familiarity evoked by novel faces that had a general resemblance to faces encountered previously. We propose that false recognition in J.S. resulted from the breakdown of strategic frontal memory retrieval, monitoring, and decision functions critical for attributing the experience of familiarity to its appropriate source.

Face memory impairments in patients with frontal lobe damage.

OBJECTIVE: To determine whether damage to prefrontal cortex is associated with face memory impairment. BACKGROUND: Neurophysiologic and functional imaging studies suggest that prefrontal cortex is a key component of a distributed neural network that mediates face recognition memory. However, there have been few attempts to examine the impact of frontal lobe damage on face memory performance. METHODS: Patients with focal frontal lobe lesions and normal control subjects were administered two-alternative forced-choice and single-probe "yes/no" tests of recognition memory for novel faces. Retrograde memory was assessed by using famous faces as stimuli. RESULTS: Compared with control subjects, patients with frontal lobe lesions showed evidence of marked anterograde and relatively mild retrograde face memory impairment. In addition, patients with right frontal lesions demonstrated increased susceptibility to false recognition, consistent with the breakdown of strategic memory retrieval, monitoring, and decision functions. CONCLUSIONS: Prefrontal cortex plays an important role in the executive control of face memory encoding and retrieval. Left and right prefrontal regions seem to make different contributions to recognition memory performance.

Fear recognition deficits after focal brain damage: a cautionary note.

OBJECTIVE: To test the hypothesis that fear recognition deficits in neurologic patients reflect damage to an emotion-specific neural network. BACKGROUND: Previous studies have suggested that the perception of fear in facial expressions is mediated by a specialized neural system that includes the amygdala and certain posterior right-hemisphere cortical regions. However, the neuropsychological findings in patients with amygdala damage are inconclusive, and the contribution of distinct cortical regions to fear perception has only been examined in one study. METHODS: We studied the recognition of six basic facial expressions by asking subjects to match these emotions with the appropriate verbal labels. RESULTS: Both normal control subjects (n = 80) and patients with focal brain damage (n = 63) performed significantly worse in recognizing fear than in recognizing any other facial emotion, with errors consisting primarily of mistaking fear for surprise. Although patients were impaired relative to control subjects in recognizing fear, we could not obtain convincing evidence that left, right, or bilateral lesions were associated with disproportionate impairments of fear perception once we adjusted for differences in overall recognition performance for the other five facial emotion categories. The proposed special role of the amygdala and posterior right-hemisphere cortical regions in fear perception was also not supported. CONCLUSIONS: Fear recognition deficits in neurologic patients may be attributable to task difficulty factors rather than damage to putative neural systems dedicated to fear perception.

Anomia for facial expressions: evidence for a category specific visual-verbal disconnection syndrome.

We describe a patient with a selective impairment in naming and pointing to emotional facial expressions following damage to the right temporal lobe. His language functions were otherwise intact, and he performed well on a variety of perceptual and associative emotional facial tasks. We propose that his inability to match facial expressions with their names was induced by a disconnection between visual semantic and verbal semantic representations for facial emotions.

Contributions of the left and right cerebral hemispheres to line bisection.

Thirty-one right-hemisphere lesioned (RHL) patients, 11 left-hemisphere lesioned patients (LHL) and 10 normal controls (NC) bisected lines in three spatial location and four directional cuing conditions. The error direction and error size were analyzed as separate and combined variables. Seventy-seven percent of RHL patients and 45% of LHL patients made abnormally large errors in line bisection. Right-hemisphere lesioned patients were more sensitive to spatial location and directional cuing than NC subjects. In contrast, LHL patients were less sensitive to either condition than NCs. The error direction and error size emerged as dissociable components of line bisection. Right-hemisphere lesioned patients and NC subjects bisected lines consistently to one side of the true center. Left-hemisphere lesioned patients bisected lines equally often on both sides of the true center. Both RHL and LHL patients made larger absolute bisection errors than NC subjects, but the RHL patient's errors were larger than those of the LHL patients. We propose that the greater sensitivity of RHL patients to spatial location and directional cues and the directional consistency of their bisection errors represent contributions of the intact left cerebral hemisphere to line bisection. In contrast, the LHL patient's unrestrained ability to orient to both ends of the line reflects a contribution of the intact right cerebral hemisphere to line bisection. The failure of both groups to accurately bisect lines reflects a common visuospatial processing deficit that is more pronounced following RHLs than LHLs.

Hierarchical stimuli and hemispheric specialization: two case studies.

Local versus global visual processing was examined in two patients with massive unilateral left hemisphere lesions using a directed attention task involving hierarchical stimuli. Previous studies found an impressive global advantage in patients with posterior left hemisphere lesions on similar tasks. In addition, whereas patients with left inferior parietal lobule (IPL) lesions showed the global interference on local processing that is typically observed in normals, patients with lesions centered on the superior temporal gyrus (STG) demonstrated no interference. Paradoxically, our two patients who had complete destruction of both the left IPL and STG regions showed an overall local advantage due to local interference on global processing. We propose that following extensive left hemisphere damage, the isolated right hemisphere may be able to perform efficiently the type of processing usually ascribed to the left hemisphere (i.e., local). However, at least under certain conditions, this apparent functional plasticity seems to occur at the expense of the type of processing normally associated with the right hemisphere (i.e., global).

False recognition of unfamiliar faces following right hemisphere damage: neuropsychological and anatomical observations.

False recognition of unfamiliar faces was investigated in patients with focal right hemisphere damage (RHD) in order to define the neuropsychological and anatomical correlates of the recognition impairment and examine its relationship to prosopagnosia. Findings are discussed within the framework of the Bruce and Young (1986) model of face processing. Although false recognition and prosopagnosia were both present in some RHD patients, the two types of face recognition impairments were dissociable in others. Processing deficits in subjects with both false recognition and prosopagnosia were associated with posterior right hemisphere lesion sites and included severe face perception impairment and partial damage to face recognition units (FRUs). Prosopagnosia without false recognition was seen following near complete destruction of FRUs, but this type of dissociation could also occur when FRUs become disconnected. The opposite dissociation, false recognition without prosopagnosia, was observed following right prefrontal damage. We propose that false recognition in frontal patients results from the breakdown of strategic decision making and monitoring functions critical for determining whether a face is indeed that of a familiar person or whether there is merely a resemblance to a known individual. False recognition following prefrontal damage may also be related to confabulation, in which case familiarity or even specific identity are erroneously attributed to facial stimuli without the activation of an underlying memory representation.

False recognition and misidentification of faces following right hemisphere damage.

We report two patients who, following massive damage to the right hemisphere, showed a striking tendency for false recognition and misidentification of faces. Neuropsychological investigations revealed that excessive reliance on a feature-based left hemisphere strategy in face processing, combined with an inability to evaluate critically the output generated by the dysfunctional face recognition system, played a major role in the recognition errors and misidentifications. Our findings suggest that the feature based left hemisphere face recognition system is potentially error-prone, presumably because component facial features are likely to be shared among several different individuals, and that reliable recognition and identification of faces is critically dependent upon the efficient processing of configurational facial information by the right hemisphere. We propose further that decision making and monitoring functions relevant to the operations of the face recognition system are primarily lateralized to the right frontal lobe.

Object memory effects on figure assignment: conscious object recognition is not necessary or sufficient.

In three experiments we investigated whether conscious object recognition is necessary or sufficient for effects of object memories on figure assignment. In experiment 1, we examined a brain-damaged participant, AD, whose conscious object recognition is severely impaired. AD's responses about figure assignment do reveal effects from memories of object structure, indicating that conscious object recognition is not necessary for these effects, and identifying the figure-ground test employed here as a new implicit test of access to memories of object structure. In experiments 2 and 3, we tested a second brain-damaged participant, WG, for whom conscious object recognition was relatively spared. Nevertheless, effects from memories of object structure on figure assignment were not evident in WG's responses about figure assignment in experiment 2, indicating that conscious object recognition is not sufficient for effects of object memories on figure assignment. WG's performance sheds light on AD's performance, and has implications for the theoretical understanding of object memory effects on figure assignment.

Disruption of semantic influence on writing following a left prefrontal lesion.

We report a patient with impaired spontaneous writing, written naming, and homophone spelling, consistent with a disruption of semantic influence on writing. However, writing to dictation by both the phonological and lexical spelling systems was intact. In addition, general semantic abilities were spared, as indicated by preserved auditory and reading comprehension. We propose that our patient could not incorporate meaning into writing because of a disruption of both direct and indirect connections between semantics and the orthographic output lexicon. The writing dysfunction was accompanied by a similar impairment of speech output, suggesting that it was part of a more general disturbance of semantic influence on language production following left prefrontal damage.