fMRI reveals large-scale network activation in minimally conscious patients

BACKGROUND

The minimally conscious state (MCS) resulting from severe brain damage refers to a subset of patients who demonstrate unequivocal, but intermittent, behavioral evidence of awareness of self or their environment. Although clinical examination may suggest residual cognitive function, neurobiological correlates of putative cognition in MCS have not been demonstrated.

OBJECTIVE

To test the hypothesis that MCS patients retain active cerebral networks that underlie cognitive function even though command following and communication abilities are inconsistent.

METHODS

fMRI was employed to investigate cortical responses to passive language and tactile stimulation in two male adults with severe brain injuries leading to MCS and in seven healthy volunteers.

RESULTS

In the case of the patient language-related tasks, auditory stimulation with personalized narratives elicited cortical activity in the superior and middle temporal gyrus. The healthy volunteers imaged during comparable passive language stimulation demonstrated responses similar to the patients' responses. However, when the narratives were presented as a time-reversed signal, and therefore without linguistic content, the MCS patients demonstrated markedly reduced responses as compared with volunteer subjects, suggesting reduced engagement for "linguistically" meaningless stimuli.

CONCLUSIONS

The first fMRI maps of cortical activity associated with language processing and tactile stimulation of patients in the minimally conscious state (MCS) are presented. These findings of active cortical networks that serve language functions suggest that some MCS patients may retain widely distributed cortical systems with potential for cognitive and sensory function despite their inability to follow simple instructions or communicate reliably.

Neurocognitive assessment before and after cranioplasty

OBJECTIVE

This paper addresses the possible value of neurocognitive tests on the evaluation of patients before and after cranioplasty for large cranial defects.

METHODS

In a single patient with a large corrected cranial defect a detailed neurocognitive analysis was performed utilizing the EXIT interview and Cognistat before and after surgery. Planning and development of the surgical prosthesis were based on the pre-operative reconstruction of the head CT and on pre-operative pictures of the patient. Xenon-CT anatomical and quantitative cerebral blood flow (CBF) analysis was performed before and periodically after cranioplasty.

FINDINGS

A significant improvement in major cognitive functions was observed after surgery.

INTERPRETATION

Cognistat is a detailed neuropsychological battery that permits a better assessment of patients in diverse neurological conditions. The EXIT interview gives a better rapid assessment of cognition not provided by other methods, such as the mini-mental status examination (MMSE). The utilization of these techniques permits a better understanding of long-term outcomes for patients with diverse neurological conditions, including post-cranioplasty patients.

Acquisition and transfer of new verbal information in amnesia: retrieval and neuroanatomical constraints

Four experiments examined new associative learning in amnesia by contrasting the performance of 2 amnesic participants-1 (C.C.) with basal forebrain damage and the other (R.H.) with medial temporal lobe damage--and 3 controls. Both amnesic individuals were severely impaired on explicit memory measures but showed intact perceptual priming. On the new associations measures, only C.C., not R.H., exhibited learning by producing correct targets (HIJACKER) in the absence of perceptual cues for them (e.g., STAFF shot ???). When the perceptual cue (e.g., MEDICINE cured _I_C_P) was provided, both C.C. and R.H. showed learning. Transfer to information containing conceptually related targets (e.g., TERRORIST or BELCH) was reliably observed only in C.C. This finding was replicated with further reduction in perceptual overlap across original (LIGHTNING torched JUNGLE) and transfer (LIGHTNING burned WILDERNESS) sentences. Together, these findings delineate the role of experimental conditions, severity of amnesia, and different neuroanatomical structures in mediating new verbal learning in amnesia.

Oedipism in a patient with frontal lobe encephalomalacia

There is a growing recognition of the role of the frontal lobes in the aetiology of severe behavioural aberrations. The authors describe a case of Oedipism in a patient who had MRI evidence of frontal lobe encephalomalacia. After discussing the function of the frontal lobes in modulating behaviour the authors suggest that the structural lesion seen on the MRI was in part responsible for the patient's self-destructive act. Treatment issues and the importance of recognizing underlying structural lesions in instances of extreme self-mutilation are discussed.