Engineered neuronal circuits shaped and interfaced with carbon nanotube microelectrode arrays.

Standard micro-fabrication techniques which were originally developed to fabricate semi-conducting electronic devices were inadvertently found to be adequate for bio-chip fabrication suited for applications such as stimulation and recording from neurons in-vitro as well as in-vivo. However, cell adhesion to conventional micro-chips is poor and chemical treatments are needed to facilitate the interaction between the device surface and the cells. Here we present novel carbon nanotube-based electrode arrays composed of cell-alluring carbon nanotube (CNT) islands. These play a double role of anchoring neurons directly and only onto the electrode sites (with no need for chemical treatments) and facilitating high fidelity electrical interfacing-recording and stimulation. This method presents an important step towards building nano-based neurochips of precisely engineered networks. These neurochips can provide unique platform for studying the activity patterns of ordered networks as well as for testing the effects of network damage and methods of network repair.

Compact self-wiring in cultured neural networks.

We present a novel approach for patterning cultured neural networks in which a particular geometry is achieved via anchoring of cell clusters (tens of cells/each) at specific positions. In addition, compact connections among pairs of clusters occur spontaneously through a single non-adherent straight bundle composed of axons and dendrites. The anchors that stabilize the cell clusters are either poly-D-lysine, a strong adhesive substrate, or carbon nanotubes. Square, triangular and circular structures of connectivity were successfully realized. Monitoring the dynamics of the forming networks in real time revealed that the self-assembly process is mainly driven by the ability of the neuronal cell clusters to move away from each other while continuously stretching a neurite bundle in between. Using the presented technique, we achieved networks with wiring regions which are made exclusively of neuronal processes unbound to the surface. The resulted network patterns are very stable and can be maintained for as long as 11 weeks. The approach can be used to build advanced neuro-chips for bio-sensing applications (e.g. drug and toxin detection) where the structure, stability and reproducibility of the networks are of great relevance.

Signal-detection analysis of group decision making.

How effectively can groups of people make yes-or-no decisions? To answer this question, we used signal-detection theory to model the behavior of groups of human participants in a visual detection task. The detection model specifies how performance depends on the group's size, the competence of the members, the correlation among members' judgments, the constraints on member interaction, and the group's decision rule. The model also allows specification of performance efficiency, which is a measure of how closely a group's performance matches the statistically optimal group. The performance of our groups was consistent with the theoretical predictions, but efficiency decreased as group size increased. This result was attributable to a decrease in the effort that members gave to their individual tasks rather than to an inefficiency in combining the information in the members' judgments.

Spreadsheet signal detection.

A number of studies in perception, attention, and memory employ signal detection theory (SDT) to assess the accuracy of an observer's detection or discrimination performance. Some of the problems that students have with understanding and using SDT are associated with the calculations needed to obtain SDT parameters and predictions. All of these calculations, plus the simulation of SDT processes, can be performed using a spreadsheet application program, such as Excel or Quattro Pro. This paper offers a short tutorial on how to use a spreadsheet program to increase your students' knowledge and understanding of SDT.

Effect of temporal position, proportional variance, and proportional duration on decision weights in temporal pattern discrimination.

Two experiments investigated how listeners allocate their attention to different segments of a temporal pattern. The experiments allowed a direct test of the predictions of the Proportion of Total Duration (PTD) rule and the Component Relative Entropy (CoRE) model. Listeners had to decide whether two sequences of nine tones had the same or different temporal patterns (tone duration = 25 ms, tone frequency = 1000 Hz). A sequence's temporal pattern was determined by the time intervals between each tone's offset and the next tone's onset. On same trials, the time intervals at corresponding temporal positions in the two sequences were identical. On different trials, the corresponding time intervals were randomly varied. Listener attention to different temporal positions within a sequence was assessed by calculating the decision weights at each position. The results supported the CoRE model and were inconsistent with the PTD rule. Manipulating the mean of the time intervals within the sequence had no consistent effect on the pattern of weights (or on overall performance), indicating that listener attention was not affected by either the proportion of total duration or the perceptual salience of a longer or shorter time interval. However, manipulating the variance of the time intervals had a significant effect: the highest weight was given to the highest variance segment. This weighting strategy leads to better performance because higher variance segments are more diagnostic of whether the sequences are the same or different.

First pass Tc-99m MIBI ventriculography in the assessment of left ventricular diastolic function. A comparison with Doppler echocardiography.

Tc-99m MIBI is used for myocardial imaging and first-pass studies. However, little is known about its utility in the assessment of left ventricular diastolic function. The authors retrospectively compared first pass studies of Tc-99m MIBI at rest with Doppler flow velocity measurements to assess left ventricular diastolic performance. Thirty-nine patients who had both studies performed within 48 hours of each other were evaluated. Three indices of diastolic function were measured by first pass Tc-99m MIBI ventriculography and Doppler echocardiography: 1) Time to peak early diastolic velocity; 2) normalized peak filling rate; and 3) half filling fraction. The results demonstrated a correlation of 0.82 (P < 0.001), 0.82 (P < 0.001), and 0.53 (P = 0.001) for the above indices, respectively. This study indicates that the indices of left ventricular diastolic function by first pass Tc-99m MIBI compare favorably with those derived from Doppler flow velocity measurements in which the diagnostic value has been previously established. Both methods accurately reflect diastolic flow and may facilitate clinical evaluation of diastolic function.

Inadvertent malposition of a transvenous-inserted pacing lead in the left ventricular chamber.

In conclusion, we propose the following approach to prevent and manage lead malposition in the left ventricle: A 12-lead electrocardiogram in the paced mode and an anterior and lateral chest view should be thoroughly inspected shortly after pacemaker implantation. A definitive diagnosis of malposition can be established with these tests. Development of any neurologic symptoms should be attributed to the malpositioned lead until proved otherwise. In such patients, serious consideration should be given to transcatheter or surgical lead extraction after a period of anticoagulation. If this is not possible, chronic anticoagulation with warfarin must be initiated, achieving an international normalized ratio of > or = 2.5. Antiplatelet therapy alone may not confer adequate protection against future cerebral events. Furthermore, most patients with neurologic manifestations do not have echocardiographic evidence of thrombus on the lead. Conversely, presence of thrombus is highly associated with neurologic symptoms. Any intraarterial lead must be removed due to inevitable complications. Patients who have remained completely asymptomatic for > or = 3 years may be followed carefully with no therapy. For asymptomatic patients diagnosed before this time period, we recommend empiric therapy with antiplatelet agents or low-dose warfarin (international normalized ratio 1.5-2) with careful observation for symptoms.

Thoracic aortic thrombosis as a cause of bowel ischemia. A case report.

Acute occlusion of the superior mesenteric artery (SMA) is a devastating disease with a high mortality rate. Among its causes is thromboembolism from the heart or from an aortic aneurysm. The authors report a sixty-four-year-old woman who sustained acute occlusion of the SMA from a very large thrombus located on the medial wall of the thoracic aorta, unrelated to an aneurysm. The thrombus was pedunculated and occupied over two thirds of the aortic lumen. Transesophageal echocardiography (TEE) proved to be a valuable tool in diagnosis. The appearance of the thrombus on computed tomographic scan very closely resembled a type B aortic dissection and may have been interpreted as such if the TEE result had not been available.

Left heart pacing and cardioembolic stroke.

Three patients with inadvertently positioned left heart pacemaker leads were admitted for neurological symptoms consistent with embolic stroke. In one of them, the pacemaker lead crossed the interatrial septum, the mitral valve, and entered the left ventricle. In another it was erroneously placed through the subclavian artery, across the aortic valve, and into the left ventricular chamber. In the third patient, the right ventricular lead of a DDD pacemaker was placed in the coronary sinus and the right atrial lead crossed the interatrial septum, and intermittently entered the left ventricular cavity. Once anticoagulation was initiated, symptoms resolved; they recurred when the level of anticoagulation dropped leading to a major stroke in one of the patients. Two of the patients were on aspirin at the onset of symptoms. We believe that every approach must be considered to remove the malpositioned lead. Otherwise, full dose anticoagulation must be initiated since antiplatelet therapy alone does not confer adequate protection against stroke.

Effect of sequence delay on the discrimination of temporal patterns.

This experiment tested listeners' ability to discriminate between two temporal patterns as a function of the time interval between the pattern onsets. The listener's task was to decide whether two arrhythmic sequences of nine tones had the same or different temporal patterns; the patterns were defined by the time intervals between the tones. According to the temporal pattern correlation model [R. D. Sorkin, J. Acoust. Soc. Am. 87, 1695-1701 (1990)], listeners extract information about the series of time intervals in each sequence and then compute the correlation between the two series. In the present experiment, the tones in the second sequence were presented at a different frequency than the tones in the first sequence. In one condition, all time intervals in the second sequence were compressed or expanded by a factor that varied randomly over trials. Performance was very good when the sequences did not overlap in time, but was poor when the sequences overlapped. Performance was generally consistent with a discrimination mechanism that cannot process more than one pattern at a time.

Effect of time compression and expansion on the discrimination of tonal patterns.

This experiment tested how well human listeners can discriminate between temporal patterns that are compressed or expanded in time. The listener's task was to determine whether two arrhythmic, tonal sequences had the same or different temporal patterns. According to the pattern correlation model [R. D. Sorkin, J. Acoust. Soc. Am. 87, 1695-1701 (1990)], listeners perform this task by computing the correlation between the pattern of time intervals marked by the tones in each sequence. Listener performance dropped when one of the sequences was compressed or expanded in time. In order for the model to describe the observed performance, it was necessary to postulate an internal noise component that was proportional to the magnitude of the difference between the sequence transformations.

Perception of temporal patterns defined by tonal sequences.

This experiment tested how listeners discriminate between the temporal patterns defined by two sequences of tones. Two arrhythmic sequences of n tones were played successively (n = 8, 12, or 16, tone duration = 35 ms, frequency = 1000 Hz), and the listener reported whether the sequences had the same or different temporal patterns. In the first sequence, the durations of the intertone gaps were chosen at random; in the second sequence, the gaps were either (a) the same as the first sequence or (b) chosen at random. Discrimination performance increased with the variability of the gap sequences and decreased with the size of the correlation between the sequences. A discrimination model based on computation of the sample correlation between the sequences of gaps, but limited by an internal variability of approximately 15 ms, described observer performance in a variety of conditions.

Temporal factors in the discrimination of tonal sequences.

Human observers were asked to judge whether or not two sequences of eight or more tones had the same serial pattern of frequencies. The temporal envelopes of the sequences were manipulated by randomly varying the tone durations or intertone gaps. In the correlated condition, the temporal envelopes of the sequences were varied across trials; the two sequences within each trial had the same temporal envelope. In the uncorrelated condition, the temporal envelopes were varied both across and within trials; every sequence had a unique temporal pattern. Performance in the uncorrelated condition decreased with increased variability in the temporal envelope. Performance in the correlated condition was independent of temporal variability, but decreased with increases in the time interval between the onsets of the two sequences. This pattern of results is consistent with an extension of a model of auditory discrimination developed by Durlach and Braida [J. Acoust. Soc. Am. 46, 372-383 (1969)], in which two processing modes are postulated: a trace mode and a context mode. When the tonal sequences had unique temporal patterns, context mode processing was dominant; when the sequences had identical temporal patterns, trace mode processing was preferred. The effect of variables such as the number of tones, the tone duration, the time gap between tones, and the time interval between sequences was consistent with the predictions of the discrimination model.

Anomalous pulmonary venous connection. Medical therapy.

Anomalous pulmonary venous connection is a congenital defect which may first be diagnosed in the adult who has developed lung disease or pulmonary vascular obstructive disease. Surgical repair may be inadvisable in such a case. To date, little attention has been paid in the literature to medical management. A case is presented in which medical palliation with nitrate therapy was successful.