Impaired associative learning in chronic fatigue syndrome

The cognitive impact of chronic low back pain: Positive effect of multidisciplinary pain therapy

Objectives

Little is known about the affected cognitive problems in chronic low back pain patients. For this patient cohort research mostly focused on memory of pain, rather than cognitive difficulties related to pain. Chronic pain may be associated with specific (yet undefined) cognitive deficits that affect everyday behaviour. We set out to compare the cognitive function of patients with chronic low back pain (cLBP) in the course of multidisciplinary pain treatments before and after therapy.

Methods

Thirty-three patients with cLBP and 25 healthy controls between 20 and 70 years were recruited into the study. The inclusion criteria for patients were: (1) a history of at least 12 weeks of chronic myofascial low back pain without radicular pain sensation before enrolment; (2) grade II and higher chronicity according to von Korff; (3) no opioid medication. The patients recruited had a mean pain duration of 7.13 ± 7.16 years and reported a mean pain intensity of 6.62 ± 2.04 (visual analogue score, VAS). Their mean back function according to the Funktionsfragebogen Hannover (FFbH, a questionnaire comparable with the Health Assessment Questionnaire) was 52.39 ± 20.23%.

At three time points (before therapy, 3 weeks and 6 months after therapy) the study subjects were assessed prospectively with a battery of visual memory tests from the Cambridge Neuropsychological Test Automated Battery (CANTAB). These included choice reaction time (CRT), pattern recognition memory (PRM) and spatial span (SSP). In parallel, the Trail-Making Test (TMT-A, TMT-B) and the Wechsler Adult Intelligence Scale (WAIS-III) were used to evaluate intelligence and cognitive flexibility.

Results

At the beginning of MDPT (T1), it took patients with cLBP significantly longer than HC to complete TMT-A (38.29 ± 19.99 s vs 30.25 ± 14.19 s, p = 0.047) and TMT-B (72.10 ± 26.98 s vs 55.99 ± 22.14 s, p = 0.034). There were no significant differences between patients and HC in CRT, PRM and SSP. Three weeks (T2) and 6 months (T3) after MDPT, TMT-A reaction time of patients significantly improved by 6.5 s and 8.1 ms (38.3 ±19.9 s vs 31.8 ±12.3 s, p = 0.02 and 31.8 ± 12.3 s vs 30.2 ± 8.9 s, p = 0.021, respectively). The patients’ working memory was also better 6 months after MDPT (48.8 ± 11.1% at T1, 51.2 ±11.9% at T2, 57.1 ±10.9% at T3, p = 0.008). Significant correlations among pain, depression/anxiety, medication and neuropsychological tests were found.

Conclusions

These findings show that patients with cLBP have slowed speeds of information processing and working memory, but no alteration in attention and recognition memory. There are clearly interactions of cognitive function with pain, depression, anxiety, and medication. MDPT may improve the impaired cognitive function of patients with cLBP.

Implication

Health professionals should contemplate the results from this study when planning therapy strategies especially when prescribing pain medications such opioids to patients with chronic low back pain.

Behaviorally inhibited individuals demonstrate significantly enhanced conditioned response acquisition under non-optimal learning conditions

Behavioral inhibition (BI) is an anxiety vulnerability factor associated with hypervigilance to novel stimuli, threat, and ambiguous cues. The progression from anxiety risk to a clinical disorder is unknown, although the acquisition of defensive learning and avoidance may be a critical feature. As the expression of avoidance is also central to anxiety development, the present study examined avoidance acquisition as a function of inhibited temperament using classical eyeblink conditioning. Individuals were classified as behaviorally inhibited (BI) or non-inhibited (NI) based on combined scores from the Adult and Retrospective Measures of Behavioural Inhibition (AMBI and RMBI, respectively). Acquisition was assessed using delay, omission, or yoked conditioning schedules of reinforcement. Omission training was identical to delay, except that the emission of an eyeblink conditioned response (CR) resulted in omission of the unconditioned airpuff stimulus (US) on that trial. Each subject in the yoked group was matched on total BI score to a subject in the omission group, and received the same schedule of CS and US delivery, resulting in a partial reinforcement training schedule. Delay conditioning elicited significantly more CRs compared to the omission and yoked contingencies, the latter two of which did not differ from each other. Thus, acquisition of an avoidance response was not apparent. BI individuals demonstrated enhanced acquisition overall, while partial reinforcement training significantly distinguished between BI and NI groups. Enhanced learning in BI may be a function of an increased defensive learning capacity, or sensitivity to uncertainty. Further work examining the influence of BI on learning acquisition is important for understanding individual differences in disorder etiology in anxiety vulnerable cohorts.

Behaviorally inhibited temperament is associated with severity of post-traumatic stress disorder symptoms and faster eyeblink conditioning in veterans

Prior studies have sometimes demonstrated facilitated acquisition of classically conditioned responses and/or resistance to extinction in post-traumatic stress disorder (PTSD). However, it is unclear whether these behaviors are acquired as a result of PTSD or exposure to trauma, or reflect preexisting risk factors that confer vulnerability for PTSD. Here, we examined classical eyeblink conditioning and extinction in veterans self-assessed for current PTSD symptoms, exposure to combat, and the personality trait of behavioral inhibition (BI), a risk factor for PTSD. A total of 128 veterans were recruited (mean age 51.2 years; 13.3% female); 126 completed self-assessment, with 25.4% reporting a history of exposure to combat and 30.9% reporting current, severe PTSD symptoms (PTSS). The severity of PTSS was correlated with current BI (R(2) = 0.497) and PTSS status could be predicted based on current BI and combat history (80.2% correct classification). A subset of the veterans (n = 87) also completed the eyeblink conditioning study. Among veterans without PTSS, childhood BI was associated with faster acquisition; veterans with PTSS showed delayed extinction, under some conditions. These data demonstrate a relationship between current BI and PTSS, and indicate that the facilitated conditioning sometimes observed in patients with PTSD may partially reflect personality traits such as childhood BI that pre-date and contribute to vulnerability for PTSD.

Facilitated acquisition of the classically conditioned eyeblink response in women taking oral contraceptives

Although anecdotal reports suggest that associative learning processes are affected by menstrual phase, empirical evidence has been equivocal. Moreover, there is a dearth of research concerning fluctuations of artificial or exogenous female hormones on learning and memory. Therefore, in this preliminary study we assessed learning in women who take oral contraceptives and those who do not during the three phases of the menstrual cycle: early, middle, and later cycle. The behavioral assessment included short-trace eyeblink conditioning, acoustic startle reactivity, and a fine motor coordination task (grooved pegboard). Oral contraceptive users generally acquired the conditioned eyeblink response better than non-users. Similar enhancements were observed for fine motor coordination and startle responsiveness. Further research will need to distinguish whether the hormone influence is upon the associative processes or the sensory-motor pathways involved in nonassociative learning.

Discriminative delay Pavlovian eyeblink conditioning in veterans with and without posttraumatic stress disorder

BACKGROUND

Impaired eyeblink (EB) classical conditioning using a delay paradigm has previously been shown in combat veterans, as well as in a group of depressed adults, compared to normal individuals. Significant deficits in immediate memory (IM) in combat PTSD+ veterans, compared to normal controls, have also been previously shown, but these differences became non-significant after controlling for level of self-reported depression. Furthermore, EB conditioning has been shown to be significantly correlated with heart rate variability (HRV) in normal adults. The present study examined how depression (self-reported), IM, and resting HRV are related to discriminative delay classical EB conditioning in veterans with and without PTSD.

METHOD

Three groups of subjects (combat PTSD+, combat PTSD-, and non-combat PTSD-) were assessed for self-report of depression and anxiety, as well as IM and HRV. Subjects received a single session of discriminative EB classical conditioning in which the conditioned stimulus (CS) was a light signal (either red or green) compounded with a tone. On CS+ trials, the light-tone compound stimulus co-terminated with a corneal airpuff (unconditioned stimulus, US), thus producing a delay paradigm. On CS- trials the appropriate light-tone stimulus was presented but not followed by the airpuff US. EB amplitude and frequency were recorded.

RESULTS

PTSD+ subjects had greater self-reported depression and anxiety scores than the two control groups, as well as lower scores on a measure of IM. However, the IM difference was not significant after the effects of self-reported depression and anxiety were controlled. EB CR amplitude was significantly greater to CS+ than CS- for all three groups. EB amplitude to both the US (airpuff) and the CS+ declined over trials, but was significantly lower in the combat PTSD+ group compared to the combined PTSD- groups. Subjects who reached an EB CR acquisition criterion had significantly greater scores on IM than those who did not reach criterion. Factor analysis of the entire data set revealed four factors corresponding to (1) self-reported depression and anxiety, (2) IM, (3) HRV, and (4) EB amplitude. EB frequency was significantly predicted by IM and HRV.

CONCLUSIONS

These data extend our previous results by showing deficits in EB conditioning among combat PTSD+ veterans that were associated with lower IM and resting HRV, but were not associated with self-report of depression.

Chronic fatigue syndrome: an update

The chronic fatigue syndrome is characterised by a fatigue that is disproportionate to the intensity of effort that is undertaken, has persisted for 6 months or longer, and has no obvious cause. Unless there has been a long period of patient- or physician-imposed inactivity, objective data may show little reduction in muscle strength or peak aerobic power, but the affected individual avoids heavy activity. The study of aetiology and treatment has been hampered by the low disease prevalence (probably <0.1% of the general population), and (until recently) by a lack of clear and standardised diagnostic criteria. It is unclear how far the aetiology is similar for athletes and nonathletes. It appears that in top competitors, overtraining and/or a negative energy balance can be precipitating factors. A wide variety of other possible causes and/or precipitating factors have been cited in the general population, including psychological stress, disorders of personality and affect, dysfunction of the hypothalamic-pituitary-adrenal axis, hormonal imbalance, nutritional deficits, immune suppression or activation and chronic infection. However, none of these factors have been observed consistently. The prognosis is poor; often disability and impairment of athletic performance are prolonged. Prevention of overtraining by careful monitoring seems the most effective approach in athletes. In those where the condition is established, treatment should aim at breaking the vicious cycle of effort avoidance, deterioration in physical condition and an increase in fatigue through a combination of encouragement and a progressive exercise programme.