The analysis of heart rate (HR) variability offers a noninvasive method to investigate autonomic nervous system activity in comatose patients. We analyzed three components of the HR variability in a group of comatose patients: the low-frequency band (LF), representing mainly sympathetic influence, the mid-frequency band (MF), representing sympathetic and parasympathetic influence, and the high-frequency band (HF), representing the parasympathetic influence. A value for sympathovagal balance was defined as LF/HF and MF/HF ratio. Moreover, the skin conductance level (SCL) and the skin conductance resistance (SCR) variability were recorded. The patient group consisted of 22 patients with traumatic brain injuries. Coma depth was assessed by the Glacow Coma Scale and artifact-free HR, SCL, and SCR were measured 75 times in the patient group. The results documented a significant gain in sympathetic nervous system activity corresponding with the state of emerging from coma. This gain was most pronounced in the HF component of the HR and in the sympathovagal balance between LF/HF. The findings in SCL and SCR variability endorsed this result. It is concluded that emerging from coma is accompanied by an increasing influence of the sympathetic nervous system on HR control. This leads to a change in the sympathovagal balance, i.e., a reintegration of parasympathetic and sympathetic activity.

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Unconscious processing of environmental stimuli has been convincingly demonstrated for a large number of neuropsychological syndromes. However, only few studies have successfully recorded on-line the activation of the autonomous or the motoric nervous systems. The activation of the motor system by unconscious stimuli would be a strong argument that information processing in the brain is not organized into two serial steps (stimulus identification first, response selection second). This would argue for parallel processes of stimuli identification routines and response selection mechanisms on the basis of only provisionally worked out stimulus features. Investigating an anosognostic patient we found electrodermal activity (EDA) and electromyographic responses (EMG) to bimanual tasks, mental imagery, and to the request to execute specific actions. But overt behavior remained hemiplegic and the patient was unable to feel any kind of control of her paralyzed left arm and hand. Generally, the data can be interpreted along the lines of a theory of two different routes to action, leaving the unconscious selection of action patterns intact, whereas the intentional triggering of overt behavior with the left hand and arm was impossible for the patient.

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Two cases of subdural hematoma associated with dural metastasis are reported. The computed tomographic and angiographic features are presented. The possible pathogenetic mechanism is discussed. Our cases support the idea of obstruction of dural capillaries by neoplastic cells and subsequent subdural bleeding.

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