Random-number generation and the menstrual cycle: preliminary evidence for a premenstrual alteration of frontal lobe functioning

The Effects of Total Sleep Deprivation on the Generation of Random Sequences of Key-Presses, Numbers and Nouns

According to a recent hypothesis, executive functions should be particularly vulnerable to the effects of total sleep deprivation. Random generation is a task that taps executive functions. In three experiments we examined the effects of total sleep deprivation on random generation of keypresses, numbers, and nouns, in particular on the suppression of prepotent responses and the selection of next responses by way of applying a local-representativeness heuristic. With random key-presses suppression of prepotent responses did not suffer from lack of sleep, but it became poorer at a sufficiently high pacing rate. In contrast, suppression of prepotent responses suffered when numbers and nouns were generated. According to these findings different types of random generation tasks involve different types of inhibitory process. With only four response alternatives, but not with larger response sets, application of the local-representativeness heuristic was impaired after a night without sleep. In terms of a simple formal model, serial-order representations of the preceding responses are used in selecting the next response only for the small response set, and not for larger response sets. Thus, serial-order representations are likely to suffer from loss of sleep. These findings strongly suggest that random generation involves multiple processes and that total sleep deprivation does not impair all sorts of executive functions, but only some.

Stroop-Type Interference in Random-Number Generation

We describe a positive correlation between the extent of sequential counting in a random-number generation task and the magnitude of the interference effect in Stroop's color-naming task. This finding is compatible with the view that both counting and reading are highly automatized processes which constitute an inevitable source of interference in randomization and Stroop paradigms, respectively. On the other hand, cognitive psychological theories proposing that a generally biased concept of randomness would be responsible for human subjects' inability to generate true random sequences do not readily account for this correlation. Literature on repetition avoidance indicates this universal effect in random generation is likewise not explainable in terms of some “biased concept of randomness.” Repetition avoidance (“spontaneous alternation”) also occurs in lower invertebrates, is largely independent of mathematical sophistication in humans, dissipates with increasing time between consecutive responses, and is diminished by amnesia. We conclude that the failure of functionally intact organisms to display random behavior is due to basic neuropsychological limitations. In neglecting these biological foundations, “concept of randomness” theories of randomization behavior lack explanatory value.

Neuropsychological performance and menstrual cycle: a literature review

Approximately 80% of all women of reproductive age experience psychological and physical changes associated with the premenstrual phase. Cognitive alterations are among the most common complaints. In this context, studies have assessed cognitive performance across the menstrual cycle in healthy women and also in women with premenstrual syndrome (PMS). The main objective of the present study was to review the literature on cognitive function in different phases of the menstrual cycle in women of reproductive age, both healthy and with PMS, in particular premenstrual dysphoric disorder (PMDD). We searched MEDLINE and LILACS databases. A total of 27 studies were selected. The studies used heterogeneous methodologies. Most studies suggested that healthy women show small fluctuations in cognitive performance across the menstrual cycle, with low performance scores in the luteal phase for visuospatial and motor skills, attention and concentration, verbal memory, visual memory, working memory, and reaction time. Among women with PMS or PMDD, low performance scores for visuospatial and motor skills, attention and concentration, verbal memory, working memory, reaction time and impulsivity were also detected in the luteal phase. Symptoms observed in PMS/PMDD patients showed low intensity, but greater when compared with healthy women. Evidence indicates fluctuations in cognitive performance in the different phases of the menstrual cycle in healthy and PMS women, with worse performance for women with PMS/PMDD in the luteal phase. However, methodological limitations prevent us from drawing solid conclusions. Further studies are needed to investigate the impact of these cognitive fluctuations on patients' daily activities.

Random Number Generation Deficit in Early Schizophrenia

Random number generation with a written response mode provides a potentially appealing marker for executive processes. Impaired performance on written random number generation tasks has been reported in chronic schizophrenic patients. However, no study has investigated whether such a deficit occurs in early schizophrenia and whether its profile and severity are similar to those in patients with chronic illness. This study investigated the ability to generate random numbers in patients with early schizophrenia ( n = 44) and a healthy control group ( n = 48). Patients were less able to maintain several production strategies and generated more stereotyped response sequences, whereas their abilities to identify randomness with an even-handed treatment of digits and to monitor the equality of occurrence of single digits appeared to remain intact. These results provide evidence that some aspects of the deficits in random number generation among chronic schizophrenic patients are also present at early psychotic episode, while some other aspects are relatively less affected in the early years.

Random noun generation in younger and older adults

We examined age-related changes of executive functions by means of random noun generation. Consistent with previous observations on random letter generation, older participants produced more prepotent responses than younger ones. In the case of random noun generation, prepotent responses are nouns of the same category as the preceding noun. In contrast to previous observations, older participants exhibited stronger repetition avoidance and a stronger tendency toward local evenness—that is, toward equal frequencies of the alternative responses even in short subsequences. These data suggest that at higher adult age inhibition of prepotent responses is impaired. In addition, strategic attentional processes of response selection are strengthened, in particular the application of a heuristic for randomness. In this sense response selection is more controlled in older than in younger adults.

Exploring number space by random digit generation

There is some evidence that human subjects preferentially select small numbers when asked to sample numbers from large intervals "at random". A retrospective analysis of single digit frequencies in 16 independent experiments with the Mental Dice Task (generation of digits 1-6 during 1 min) confirmed the occurrence of small-number biases (SNBs) in 488 healthy subjects. A subset of these experiments suggested a spatial nature of this bias in the sense of a "leftward" shift along the number line. First, individual SNBs were correlated with leftward deviations in a number line bisection task (but unrelated to the bisection of physical lines). Second, in 20 men, the magnitude of SNBs significantly correlated with leftward attentional biases in the judgment of chimeric faces. Finally, cognitive activation of the right hemisphere enhanced SNBs in 20 different men, while left hemisphere activation reduced them. Together, these findings provide support for a spatial component in random number generation. Specifically, they allow an interpretation of SNBs in terms of "pseudoneglect in number space." We recommend the use of random digit generation for future explorations of spatial-attentional asymmetries in numerical processing and discuss methodological issues relevant to prospective designs.

Performance in a test demanding prefrontal functions is favored by early luteal phase progesterone: an electroencephalographic study

There are some psychological studies showing changes in intellectual efficiency before and during menstruation. Many women report that they experience a feeling of difficulty to initiate activities, confront challenging situations and lack of concentration suggesting transient changes in frontal lobe functions related with gonadal hormone levels. Therefore, performance of a task demanding prefrontal functions, the Wisconsin Card Sorting Test, with simultaneous recording of electroencephalographic (EEG) activity was assessed in 9 healthy women, in a repeated measure study, during ovulation (OVU), early luteal (EL), late luteal (LL) and menstrual (MEN) phases. Spectral power of base line and task EEG, and number of responses to reach successful and unsuccessful outcomes in the task were evaluated. Performance was impaired to a certain degree during the OVU phase and was associated with an attenuated alpha1 power and with an increase of the theta and beta2 power. Performance was better during EL phase, when progesterone level is at its highest, no significant changes were observed from BL to task. Performance was worse during LL phase when hormone levels are at its lowest and was associated with a decrease in beta1 and beta2 power together with a significant attenuation of alpha1 and alpha2 power. During MEN phase performance was also improved and was associated with a significant decrease of alpha1 and alpha2 power and no changes in beta power were observed. These findings show that performance of a task demanding internal attention and planning is modulated by physiological progesterone and estrogen levels during menstrual cycle and is associated with specific EEG profiles.

Random number generation deficit in schizophrenia characterized by oral vs written response modes

To characterize the deficit in random number generation in schizophrenia with respect to control of sensory information processing, the present study employed a random number generation task using 10 digits (0 to 9) and compared two response modes (oral and written) with different amounts of sensory availability about the previous choices of the subject. Analysis indicated that the increased availability of previous information in the written response mode may exacerbate an aspect of the deficit in random number generation in schizophrenia reflecting the disturbance in control of sensory information processing. The comparison of performance in written and oral response modes may be useful in assessing schizophrenic psychopathology.

Neuropsychological performance across the menstrual cycle in women with and without Premenstrual Dysphoric Disorder

This study examined neuropsychological performance across the menstrual cycle in women with varying levels of premenstrual symptomatology. Following a 2-month period of prospective symptom documentation, there were 19 women who met DSM-IV criteria for Premenstrual Dysphoric Disorder (PMDD group) and 18 women with mild to moderate symptoms. Neuropsychological functioning was evaluated at the late follicular (pre-ovulatory) and late luteal (premenstrual) phases across the domains of psychomotor speed, attention, and verbal learning and memory. Repeated measures analysis of variance yielded significant group x phase differences on the psychomotor index, with women in the PMDD group demonstrating significant psychomotor slowing in the late luteal phase. This psychomotor slowing was subtle, however, and scores remained within the normal range across testing sessions. No group or phase differences were found on indices of attention or verbal learning and memory. These results suggest that with the exception of subtle psychomotor slowing in the late follicular relative to the late luteal phase, there is no discernible difference in cognitive functioning between women with and without PMDD.

Random motor generation in a finger tapping task: influence of spatial contingency and of cortical and subcortical hemispheric brain lesions

OBJECTIVE

To test the hypothesis that, during random motor generation, the spatial contingencies inherent to the task would induce additional preferences in normal subjects, shifting their performances farther from randomness. By contrast, perceptual or executive dysfunction could alter these task related biases in patients with brain damage.

METHODS

Two groups of patients, with right and left focal brain lesions, as well as 25 right handed subjects matched for age and handedness were asked to execute a random choice motor task--namely, to generate a random series of 180 button presses from a set of 10 keys placed vertically in front of them.

RESULTS

In the control group, as in the left brain lesion group, motor generation was subject to deviations from theoretical expected randomness, similar to those when numbers are generated mentally, as immediate repetitions (successive presses on the same key) are avoided. However, the distribution of button presses was also contingent on the topographic disposition of the keys: the central keys were chosen more often than those placed at extreme positions. Small distances were favoured, particularly with the left hand. These patterns were influenced by implicit strategies and task related contingencies. By contrast, right brain lesion patients with frontal involvement tended to show a more square distribution of key presses--that is, the number of key presses tended to be more equally distributed. The strategies were also altered by brain lesions: the number of immediate repetitions was more frequent when the lesion involved the right frontal areas yielding a random generation nearer to expected theoretical randomness. The frequency of adjacent key presses was increased by right anterior and left posterior cortical as well as by right subcortical lesions, but decreased by left subcortical lesions.

CONCLUSIONS

Depending on the side of the lesion and the degree of cortical-subcortical involvement, the deficits take on a different aspect and direct repetions and adjacent key presses have different patterns of alterations. Motor random generation is therefore a complex task which seems to necessitate the participation of numerous cerebral structures, among which those situated in the right frontal, left posterior, and subcortical regions have a predominant role.

Variables that influence the generation of random sequences: an update

This article updates Tune's 1964 review of variables influencing human subjects' attempts at generating random sequences of alternatives. It also covers aspects not included in the original review such as randomization behavior by patients with neurological and psychiatric disorders. Relevant work from animal research (spontaneous alternation paradigm) is considered as well. It is conjectured that Tune's explanation of sequential nonrandomness in terms of a limited capacity of short-term memory can no longer be maintained. Rather, interdependence among consecutive choices is considered a consequence of an organism's natural susceptibility to interference. Random generation is thus a complex action which demands complete suppression of any rule-governed behavior. It possibly relies on functions of the frontal lobes but cannot otherwise be "localized" to restricted regions of the brain. Possible developments in the field are briefly discussed, both with respect to basic experiments regarding the nature of behavioral nonrandomness and to potential applications of random-generation tasks.

Random number generation in dementia of the Alzheimer type: a test of frontal executive functions

The quality of attempts at generating a random sequence of the numbers 1-6 was studied in 30 patients with dementia of the Alzheimer type (DAT) and 30 elderly normal control (NC) subjects. Three main findings emerged: (1) DAT patients' subjective random sequences were more streotyped (contained fewer digit combinations) than those of NC subjects. (2) This difference in response stereotypy was due to patients' enhanced tendency to arrange consecutive numbers in an ascending series ('counting bias'). (3) In the patient group, degree of sequential nonrandomness was positively correlated with overall severity of dementia and with the extent to which performance on neuropsychological tests specifically assessing executive functions (fluency, naming, error monitoring) was impaired. These results illustrate a loss of behavioral complexity in the course of dementia and are interpreted as reflecting a frontal dysexecutive syndrome in DAT.