Yu-Tai Tsai

Electrical stimulation of the anterior nucleus of the thalamus for intractable epilepsy: a long-term follow-up study.

Summary:  Purpose: The anterior nucleus of the thalamus (ANT) modulates temporal lobe and hypothalamic activities, and relays information to the cingulate gyrus and entorhinal cortex. Deep brain stimulation (DBS) of the ANT has been reported to decrease seizure activity in a limited number of human subjects. However, long‐term effect of chronic ANT stimulation on such patients remains unknown. We report long‐term follow‐up results in four patients receiving ANT stimulation for intractable epilepsy.

Detection of neuronal spikes using an adaptive threshold based on the max–min spread sorting method

Neuronal spike information can be used to correlate neuronal activity to various stimuli, to find target neural areas for deep brain stimulation, and to decode intended motor command for brain-machine interface. Typically, spike detection is performed based on the adaptive thresholds determined by running root-mean-square (RMS) value of the signal. Yet conventional detection methods are susceptible to threshold fluctuations caused by neuronal spike intensity. In the present study we propose a novel adaptive threshold based on the max-min spread sorting method. On the basis of microelectrode recording signals and simulated signals with Gaussian noises and colored noises, the novel method had the smallest threshold variations, and similar or better spike detection performance than either the RMS-based method or other improved methods. Moreover, the detection method described in this paper uses the reduced features of raw signal to determine the threshold, thereby giving a simple data manipulation that is beneficial for reducing the computational load when dealing with very large amounts of data (as multi-electrode recordings).

Contact heat evoked potentials in normal subjects.

Laser-evoked potentials are widely used to investigate nociceptive pathways. The newly developed contact heat stimulator for evoking brain response has the advantages of obtaining reliable scalp potentials and absence of cutaneous lesions. This study aimed to identify the most appropriate stimulation site with consistent cortical responses, and to correlate several parameters of the contact heat evoked potentials (CHEPs) with age, gender, and body height in normal subjects. CHEPs were recorded at Cz with a contact heat stimulator (Medoc, Israel) in 35 normal controls. The subjects were asked to keep eyes open and remain alert. The baseline temperature was 32 degrees C, and stimulation peak heat intensity of 51 degrees C was applied to five body sites: bilateral forearm, right dorsum hand, right peroneal area, and right dorsum foot. Reproducible CHEPs were recorded more frequently when stimulated at volar forearm (62.5%) than at the lower limbs (around 40%). The first negative peak latency (N1) was 370.1 +/- 20.3 ms, first positive peak latency (P1) was 502.4 +/- 33.0 ms, and peak to peak amplitude was 10.2 +/- 4.9 microV with stimulation of the forearm. Perceived pain intensity was not correlated with the presence or amplitude of CHEPs. No gender or inter-side differences were observed for N1 latency and N1-P1 amplitude. Also, no correlation was noted between N1 and age or body height. These results support future clinical access of CHEPs as a diagnostic tool.

The removal of ocular artifacts from EEG signals using adaptive filters based on ocular source components.

Ocular artifacts are the most important form of interference in electroencephalogram (EEG) signals. An adaptive filter based on reference signals from an electrooculogram (EOG) can reduce ocular interference, but collecting EOG signals during a long-term EEG recording is inconvenient and uncomfortable for the patient. In contrast, blind source separation (BSS) is a method of decomposing multiple EEG channels into an equal number of source components (SCs) by independent component analysis. The ocular artifacts significantly contribute to some SCs but not others, so uncontaminated EEG signals can be obtained by discarding some or all of the affected SCs and re-mixing the remaining components. BSS can be performed without EOG data. This study presents a novel ocular-artifact removal method based on adaptive filtering using reference signals from the ocular SCs, which avoids the need for parallel EOG recordings. Based on the simulated EEG data derived from eight subjects, the new method achieved lower spectral errors and higher correlations between original uncorrupted samples and corrected samples than the adaptive filter using EOG signals and the standard BSS method, which demonstrated a better ocular-artifact reduction by the proposed method.

Unsupervised wavelet-based spike sorting with dynamic codebook searching and replenishment

Spike information is beneficial for correlating neuronal activity to various stimuli, finding target neural areas for deep brain stimulation, and decoding intended motor command for brain-machine interface. Unsupervised classification based on spike features provides a way to separate spikes generated from different neurons. Here, we propose an unsupervised spike sorting method based on specific wavelet coefficients (SWC) and using both a new spike alignment technique based on multi-peak energy comparison (MPEC) and a dynamic codebook-based template-matching algorithm with a class-merging feature. The MPEC alignment reduced inconsistent alignment caused by spike deformation. Using SWC not only reduced the number of features but also performed better in terms of matching a neuronal spike to its own class than relying on spike waveform or whole wavelet coefficients. Moreover, the employed codebook searching and replenishment can be operated in an online, real-time mode.

Complex analysis of neuronal spike trains of deep brain nuclei in patients with Parkinson's disease.

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) has been used to alleviate symptoms of Parkinsons disease. During image-guided stereotactic surgery, signals from microelectrode recordings are used to distinguish the STN from adjacent areas, particularly from the substantia nigra pars reticulata (SNr). Neuronal firing patterns based on interspike intervals (ISI) are commonly used. In the present study, arrival time-based measures, including Lempel-Ziv complexity and deviation-from-Poisson index were employed. Our results revealed significant differences in the arrival time-based measures among non-motor STN, motor STN and SNr and better discrimination than the ISI-based measures. The larger deviations from the Poisson process in the SNr implied less complex dynamics of neuronal discharges. If spike classification was not used, the arrival time-based measures still produced statistical differences among STN subdivisions and SNr, but the ISI-based measures only showed significant differences between motor and non-motor STN. Arrival time-based measures are less affected by spike misclassifications, and may be used as an adjunct for the identification of the STN during microelectrode targeting.

Significant thalamocortical coherence of sleep spindle, theta, delta, and slow oscillations in NREM sleep: Recordings from the human thalamus

The electrophysiological studies of thalamocortical oscillations were mostly done in animal models. Placement of stimulation electrodes at the anterior nucleus of the thalamus (ANT) for seizure reduction enables the study of the thalamocortical interplay in human subjects. Nocturnal sleep electroencephalograms (EEGs) and local field potentials (LFPs) of the left and right thalamus (LT, RT) were recorded in three subjects receiving ANT stimulation. Sleep stages were scored according to American Academy of Sleep Medicine criteria. The whole-night time-frequency coherence maps between EEG (C3, C4) and LFP (LT, RT) showed specific coherence patterns during non-rapid eye movement (NREM) sleep. Pooled coherence in the NREM stage was significant in slow, delta, theta and spindle frequency ranges. The spindle oscillations had the highest coherence (0.17-0.58) in the homolateral hemisphere. Together, these observations indicate that the oscillations were related to thalamocortical circuitry.

Brain connectivity of patients with Alzheimer's disease by coherence and cross mutual information of electroencephalograms during photic stimulation.

Alzheimers disease (AD) is a neurodegenerative disease, usually diagnosed by neuropsychological tests, and excluded from other cerebral diseases by brain images. An electroencephalogram (EEG) provides a means of disclosing the reduced functional couplings between brain regions that occurs with AD. In the present study, 16 probable AD patients and 15 age-matched, gender-matched normal subjects were enrolled. Spectral coherence and cross mutual information (CMI) were used to analyze EEGs during intermittent photic stimulation (PS). Ocular- and heartbeat-related source components (SCs) obtained from multi-channel EEGs by the independent component analysis were discarded, and the photic-related SCs were reduced using a comb filter. The undisturbed SCs and photic-related SCs before and after photic reduction were used to reconstruct photic-preserved EEGs and photic-reduced EEGs, from which harmonic coherences (direct photic-driving response) and rhythmic coherences and CMI (indirect photic affection) were computed, respectively. Our results indicate that the rhythmic coherences (particularly in the alpha and beta bands) and CMI variables as well as the harmonic coherences (particularly related to 3-Hz PS) were significantly lower in the probable AD than in normal subjects, whereas the variables derived from the resting EEGs were not statistically significant. This finding implied that the variables obtained during PS could be used to disclose impaired intra-brain associations in probable AD.

EPA-0098 - Perceived reasons for, opinions about, and suggestions for elders considering suicide: elderly outpatients’ perspectives

Objectives The purposes of this study were to explore elderly outpatients’ perceived reasons for, opinions of, and suggestions for elderly people considering suicide in Taiwan. Methods Elderly outpatients (N=83) were recruited in 2011-2012 by convenience sampling from three randomly selected medical centers in Taiwan. Data were collected in individual interviews using a semi-structured guide and analyzed by content analysis. Results Findings revealed that most participants had heard of elderly suicide, with television news as the main source for their information. Their opinions about elderly suicide reflected judgmental attitudes, negative emotional reactions, expectations of social welfare, and could happen after losing ones meaning in life. Their suggestions for elderly people considering suicide fell into four major themes: give up suicidal ideas, seek help, enhance social welfare, and attend religious activities. Conclusion Since television news was the main source for participants’ information about elderly suicide, this mass medium should be used in suicide prevention to disseminate suicide knowledge, increase access to help, and strengthen suicide-protective factors among the elderly. Furthermore, no participants mentioned depression as a reason for attempted or completed suicide among older people despite depression being a well-known suicide-risk factor. Future suicide-prevention programs should emphasize the role of depression in suicide among older people. Participants also did not suggest that older people considering suicide seek help from the health system. Thus, older people should be educated about the role of the health system in suicide prevention and trained as gatekeepers to recognize signs of suicide ideation and respond appropriately.

479 – Opinions about elderly suicide and reasons for not killing oneself among community-dwelling young-old Chinese elders

Background Suicide rates are high for older persons worldwide. However, no literature could be found on young-old people’s opinions about elderly suicide and the beliefs/expectations that protect them from attempting suicide. Objectives To explore opinions about elderly suicide among community-dwelling young-old people in Taiwan and their reasons for not killing themselves. Method A qualitative descriptive design was used. Young-old (65–74 years old) outpatients were recruited by convenience from two randomly selected medical centers in northern Taiwan if they had never expressed suicidal ideas and had no severe cognitive deficit. Data were collected in individual interviews and analysed by content analysis. Results Among 31 participating young-old people, most participants (87.1%) had heard of elderly suicide. Their opinions about elderly suicide reflected negative emotional reactions (32.3%), judgmental attitudes (32.3%), could happen after losing the meaning of life (9.7%), and expectations of social welfare (9.7%). Reasons for not killing themselves fell into six major themes: living well (32.3%), suicide cannot resolve problems (22.6%), fear of humiliating their children (16.1%), religious beliefs (12.9%), never thought about suicide (12.9%), and living in harmony with nature (12.9%). Conclusion Among the factors that prevented participants from killing themselves, perceptions of living well and of children’s filial behavior, as well as rational thinking could be adjusted. These factors can be addressed and improved by healthcare providers and policy makers to prevent suicide among the young-old. Our findings may also serve as a reference for geriatric researchers in western countries with increasing numbers of elderly ethnic minority immigrants.