Animal studies have shown robust electrophysiological activity in the sensory cortex in the absence of stimuli or tasks. Similarly, recent human functional magnetic resonance imaging (fMRI) revealed widespread, spontaneously emerging cortical fluctuations. However, it is unknown what neuronal dynamics underlie this spontaneous activity in the human brain. Here we studied this issue by combining bilateral single-unit, local field potentials (LFPs) and intracranial electrocorticography (ECoG) recordings in individuals undergoing clinical monitoring. We found slow (<0.1 Hz, following 1/f-like profiles) spontaneous fluctuations of neuronal activity with significant interhemispheric correlations. These fluctuations were evident mainly in neuronal firing rates and in gamma (40-100 Hz) LFP power modulations. Notably, the interhemispheric correlations were enhanced during rapid eye movement and stage 2 sleep. Multiple intracranial ECoG recordings revealed clear selectivity for functional networks in the spontaneous gamma LFP power modulations. Our results point to slow spontaneous modulations in firing rate and gamma LFP as the likely correlates of spontaneous fMRI fluctuations in the human sensory cortex.The neuronal events occurring in the sensory cortex when no stimulus is presented are not well understood. Contrary to traditional feed-forward models of information processing, a growing body of single-unit, LFP, electroencephalography (EEG), and optical imaging data point to robust levels of spontaneous neuronal activity in sensory areas of the mammalian cortex 1-7 . The modulation of such spontaneous neuronal activity can occur on very slow time scales 8, 9 . These robust spontaneous waves pose a challenge for models linking neuronal activity and sensory perception 10,11 , namely in explaining how the brain distinguishes between spontaneous events and vivid sensory percepts. One possibility is that the precise neuronal dynamics differ substantially between spontaneous and sensory-evoked conditions. This

SUMMARY Human recognition performance is characterized by abrupt changes in perceptual states. Understanding the neuronal dynamics underlying such transitions could provide important insights into mechanisms of recognition and perceptual awareness. Here we examined patients monitored for clinical purposes with multiple subdural electrodes. The patients participated in a backward masking experiment in which pictures of various object categories were presented briefly followed by a mask. We recorded ECoG from 445 electrodes placed in 11 patients. We found a striking increase in gamma power (30–70 Hz) and evoked responses specifically associated with successful recognition. The enhanced activation occurred 150–200 ms after stimulus onset and consistently outlasted the stimulus presentation. We propose that the gamma and evoked potential activations reflect a rapid increase in recurrent neuronal activity that plays a critical role in the emergence of a recognizable visual percept in conscious awareness.

Whereas visual hallucinations are often found among patients with Parkinson's disease, the occurrence of auditory hallucinations has never been systematically documented. The occurrence, past and present, of auditory hallucinations has been studied in 121 consecutive patients with Parkinson's disease attending a movement disorders clinic. The cognitive state was evaluated using the short mental test (SMT).Hallucinations were reported for 45 patients (37%); 35 (29%) had only visual hallucinations and 10 (8%) both visual and auditory hallucinations. No patient reported auditory hallucinations unaccompanied by visual hallucinations. The auditory hallucinations occurred repeatedly, consisting of human voices. They were non-imperative (n=9), non-paranoid (n=9), and often incomprehensible (n=5). They were not obviously influenced by the patients' age, duration of disease, or treatment with levodopa. Cognitive impairment was more common among hallucinating patients (64%, 50%, and 25% among patients with visual hallucinations, auditory hallucinations, and nonhallucinating parkinsonian patients respectively). Depression necessitating antidepressants was present in five of 10 and other psychotic features in six patients with auditory hallucinations.It is concluded that auditory hallucinations occur in Parkinson's disease, particularly in patients who also have visual hallucinations and are cognitively impaired. (J Neurol Neurosurg Psychiatry 1998;64:533-535)

The unpredictable and random occurrence of seizures is of the most distressful issue affecting patients and their families. Unattended seizures can have serious consequences including injury or death. The objective of this study is to develop a small, portable, wearable device capable of detecting seizures and alerting patients and families on recognition of specific seizures' motor activity. Ictal data were prospectively obtained in consecutive patients admitted to two video-EEG units. This study included patients with a history of motor seizures, clonic or tonic, or tonic-clonic seizures or patients with complex partial seizures with frequent secondary generalization. A "Motion Sensor" unit mounted on a bracelet was attached to one wrist. The "Sensor" contains a three-axis accelerometer and a transmitter. The three-axis movements' data were transmitted to a portable computer. Algorithm specially developed for this purpose analyzed the recorded data. Seizures' alerts were compared with the video-EEG data. Ictal data were acquired in 15 of the 31 recruited patients. The algorithm correctly identified 20 of 22 (91%) captured seizures and generated an alarm within a median period of 17 seconds. All events lasting >30 seconds (i.e., 19 events) were identified. The system failed to identify 2 of 22 seizures (9%). There were eight false alarms during 1,692 hours of monitoring. Preliminary data suggest that this motion detection device/alarm system can identify most motor seizures with high sensitivity and with a low false alarm rate.