Saccadic latency in hepatic encephalopathy: a pilot study

Minimal hepatic encephalopathy is associated to alterations in eye movements

Minimal hepatic encephalopathy (MHE) is diagnosed using PHES battery, but other tests are more sensitive, and a simple tool for early MHE detection is required. Assessment of saccadic eye movements is useful for early detection of cognitive alterations in different pathologies. We characterized the alterations in saccadic eye movements in MHE patients, its relationship with cognitive alterations and its utility for MHE diagnosis. One-hundred and eighteen cirrhotic patients (86 without and 32 with MHE) and 35 controls performed PHES and Stroop test and an eye movements test battery by OSCANN system: visual saccades, antisaccades, memory-guided saccades, fixation test and smooth pursuit. We analyzed 177 parameters of eye movements, assessed their diagnostic capacity for MHE, and correlated with cognitive alterations. MHE patients showed alterations in 56 of the 177 variables of eye movements compared to NMHE patients. MHE patients showed longer latencies and worse performance in most eye movements tests, which correlated with mental processing speed and attention impairments. The best correlations found were for antisaccades and memory-guided saccades, and some parameters in these tests could be useful for discriminating MHE and NMHE patients. Eye movements analysis could be a new, rapid, reliable, objective, and reproducible tool for early diagnose MHE.

Measurement of Saccade Parameters in Relation to Adaptation to Homonymous Hemianopia

Purpose:

To report saccade parameters in participants during adaptation to post-stroke homonymous hemianopia.

Methods:

In a prospective observational case cohort study, adult stroke survivors with new onset homonymous hemianopia were recruited. Using quantitative measurement, saccade parameters were measured and compared between the hemianopic and non-hemianopic sides. Two participants with longitudinal measurements were compared with age-matched controls.

Results:

Of 144 clinical study participants, quantitative saccade measurements were only possible in 14 due to an inability to visualise targets on the hemianopic side in the majority. In 9 of the 14 participants, at four weeks post-stroke, mean (±SD) saccade latency was significantly longer to the hemianopic (328.4 ± 105.9 ms) compared to the non-hemianopic side (234.7 ± SD53.6 ms; t = 4.2, df = 8, p = 0.003). The number of correct saccadic responses out of 50 was significantly lower to the hemianopic side (36.6 ± SD14.1) in comparison to the non-hemianopic side (44.4 ± SD7.5; t = –3.1, df = 8, p = 0.014). In two participants studied over an eight-week time period, saccadic differences to the hemianopic side persisted despite apparent recovery of visual field.

Conclusion:

As participants with residual visual field loss were unable to perform quantitative assessments, the widespread use of this approach in this setting is limited. However, in those whom measurements were possible, there were statistically significant differences in saccade parameters between hemianopic and non-hemianopic sides that persisted post-visual recovery. Exploration of saccades in relation to adaptation to hemianopia and response to saccadic scanning/search training requires further examination.

A novel method: can stapedial acoustic reflex have a role in the diagnosis of minimal hepatic encephalopathy?

OBJECTIVE

Stapedial acoustic reflex is an easily accessible and applicable test which is also valuable for the clinical conditions which affect the various locations of the central nervous system. Searching the diagnostic value of stapedial acoustic reflex at minimal hepatic encephalopathy is the aim of this research.

METHODS

Diagnosis of minimal hepatic encephalopathy was conducted by mini-mental state and critical flickered frequency tests. Minimal hepatic encephalopathy diagnosed patients were established in the first group. Cirrhosis (without minimal hepatic encephalopathy or overt hepatic encephalopathy) diagnosed patients were created the control group. The stapedial acoustic reflex test was applied for minimal hepatic encephalopathy and the control group by audiologists in a soundproof room.

RESULTS

In total, 221 patients were screened and 97 patients meet the inclusion criterions. Out of 97 patients, 52 were the minimal hepatic encephalopathy patients and the remaining patients were the control group. Acoustic reflex tests battery includes the evaluation of two pathways called ipsilateral and contralateral. Ipsilateral way test results were found positive in all minimal hepatic encephalopathy patients and 95% positive in the control group. Contralateral acoustic reflex test results were found 36% positive in minimal hepatic encephalopathy patients and 95% positive in the control group, respectively. A comparison of ipsilateral and contralateral acoustic reflex test results was displayed a statistical significance.

CONCLUSION

Stapedial acoustic reflex test results of cirrhosis patients may cover additional parameters for the diagnosis of minimal hepatic encephalopathy.

Ultrafast initiation of a neural race by impending errors

KEY POINTS

The brain makes decisions by means of races between neural units representing alternative choices. In the present study, we record the eyemovements made in the Wheeless task, when a visual stimulus is followed after a short delay by another stimulus demanding a different response. The behaviour can be very precisely described as a race between three independent decision processes: one Go process for each of the responses, and a Stop process that tries to cancel the first, now erroneous, response. To explain the high success rate for cancellation that we observe, the onset time for the Stop process must be some 10-20 ms shorter than for Go. As well as extending our understanding of the dynamics of complex decision-making, this task provides a rapid, non-invasive method for quantifying disorders of higher neural function.

ABSTRACT

The brain makes decisions by means of races between neural units representing alternative choices, and such models can predict behaviour in decision tasks in a precisely quantitative way. But what is less clear is how soon after the stimulus the race actually starts. In the present study, we re-visit a complex decision experiment: the Wheeless task, in which a saccadic stimulus is followed after a short delay by a second stimulus, with the subject sometimes making a saccade to the first, now inappropriate, stimulus, and sometimes going straight to the correct one. We demonstrate that a simple model with three accumulator units, two 'Go' and one 'Stop', can then account in detail for the individual responses made, as well as their timing. This complex decision-making behaviour is predicted directly for each individual subject by their performance in a simple step saccadic task, which identifies the two free parameters that are specific for each subject. By contrast to previous assumptions, we find that it is necessary for the onset time of the Stop unit to be shorter than for Go by 10-20 ms. This suggests a specifically fast mechanism for altering responses in situations where urgent action is needed to prevent an impending error.

Using saccades to diagnose covert hepatic encephalopathy

Covert Hepatic Encephalopathy (CHE), previously known as Minimal Hepatic Encephalopathy, is a subtle cognitive defect found in 30-70 % of cirrhosis patients. It has been linked to poor quality of life, impaired fitness to drive, and increased mortality: treatment is possible. Despite its clinical significance, diagnosis relies on psychometric tests that have proved unsuitable for use in a clinical setting. We investigated whether measurement of saccadic latency distributions might be a viable alternative. We collected data on 35 cirrhosis patients at Addenbrooke's Hospital, Cambridge, with no evidence of clinically overt encephalopathy, and 36 age-matched healthy controls. Performance on standard psychometric tests was evaluated to determine those patients with CHE as defined by the World Congress of Gastroenterology. We then compared visually-evoked saccades between those with CHE and those without, as well as reviewing blood test results and correlating saccadic latencies with biochemical parameters and prognostic scores. Cirrhosis patients have significantly longer median saccadic latencies than healthy controls. Those with CHE had significantly prolonged saccadic latencies when compared with those without CHE. Analysis of a cirrhosis patient's saccades can diagnose CHE with a sensitivity of 75 % and a specificity of 75 %. We concluded that analysis of a cirrhosis patient's saccadic latency distributions is a fast and objective measure that can be used as a diagnostic tool for CHE. This improved early diagnosis could direct avoidance of high-risk activities such as driving, and better inform treatment strategies.

Variability in the decision process leading to saccades: a specific marker for schizophrenia?

In a previous study, deviance in the reaction time (RT) distribution of saccades for patients with schizophrenia was explained using an oculomotor decision model. Here, RTs of visually guided saccades in young healthy men, healthy children, older adults, patients with schizophrenia, and patients with obsessive compulsive disorder (OCD) were modeled to study the specificity of this decision process deviance for schizophrenia. The mean decision rate to saccade decreased with age in children and increased in older adults while the decision rate intrasubject variability (ISV) was not modulated by age. A significant increase in ISV of the decision rate was confirmed for patients with schizophrenia but not OCD compared to healthy controls. There was no effect of medication on model parameters in the OCD patient group. These results confirm the specificity of the deviance in a simple oculomotor decision process in schizophrenia.

An internationally standardised antisaccade protocol

Detailed measurements of saccadic latency--the time taken to make an eye movement to a suddenly-presented visual target--have proved a valuable source of detailed and quantitative information in a wide range of neurological conditions, as well as shedding light on the mechanisms of decision, currently of intense interest to cognitive neuroscientists. However, there is no doubt that more complex oculomotor tasks, and in particular the antisaccade task in which a participant must make a saccade in the opposite direction to the target, are potentially more sensitive indicators of neurological dysfunction, particularly in neurodegenerative conditions. But two obstacles currently hinder their widespread adoption for this purpose. First, that much of the potential information from antisaccade experiments, notably about latency distribution and amplitude, is typically thrown away. Second, that there is no standardised protocol for carrying out antisaccade experiments, so that results from one laboratory cannot easily be compared with those from another. This paper, the outcome of a recent international meeting of oculomotor scientists and clinicians with an unusually wide experience of such measurements, sets out a proposed protocol for clinical antisaccade trials: its adoption will greatly enhance the clinical and scientific benefits of making these kinds of measurements.