Individual Resonant Frequencies at Low-Gamma Range and Cognitive Processing Speed.

Brain electrophysiological activity within the low gamma frequencies (30-80 Hz) has been proposed to reflect information encoding and transfer processes. The 40-Hz auditory steady-state response (40-Hz ASSR) is frequently discussed in relation to changed cognitive processing in neuropsychiatric disorders. However, the relationship between ASSRs and cognitive functioning still remains unclear. Most of the studies assessed the single frequency ASSR, while the individual resonance frequency in the gamma range (30-60 Hz), also called individual gamma frequency (IGF), has received limited attention thus far. Nevertheless, IGF potentially might better reflect individual network characteristics than standardly utilized 40-Hz ASSRs. Here, we focused on the processing speed across different types of cognitive tasks and explored its relationship with responses at 40 Hz and at IGFs in an attempt to uncover how IGFs relate to certain aspects of cognitive functioning. We show that gamma activity is related to the performance speed on complex cognitive task tapping planning and problem solving, both when responses at 40 Hz and at IGFs were evaluated. With the individualized approach, the observed associations were found to be somewhat stronger, and the association seemed to primarily reflect individual differences in higher-order cognitive processing. These findings have important implications for the interpretation of gamma activity in neuropsychiatric disorders.

Gamma-Range Auditory Steady-State Responses and Cognitive Performance: A Systematic Review.

The auditory steady-state response (ASSR) is a result of entrainment of the brain's oscillatory activity to the frequency and phase of temporally modulated stimuli. Gamma-range ASSRs are utilized to observe the dysfunctions of brain-synchronization abilities in neuropsychiatric and developmental disorders with cognitive symptoms. However, the link between gamma-range ASSRs and cognitive functioning is not clear. We systematically reviewed existing findings on the associations between gamma-range ASSRs and cognitive functions in patients with neuropsychiatric or developmental disorders and healthy subjects. The literature search yielded 1597 articles. After excluding duplicates and assessing eligibility, 22 articles were included. In healthy participants, the gamma-range ASSR was related to cognitive flexibility and reasoning as measured by complex tasks and behavioral indicators of processing speed. In patients with schizophrenia, the studies that reported correlations found a higher ASSR to be accompanied by better performance on short-term memory tasks, long-term/semantic memory, and simple speeded tasks. The main findings indicate that individual differences in the gamma-range ASSR reflect the level of attentional control and the ability to temporary store and manipulate the information, which are necessary for a wide range of complex cognitive activities, including language, in both healthy and impaired populations.

40-Hz auditory steady-state responses and the complex information processing: An exploratory study in healthy young males.

Electroencephalographic (EEG) activity in the gamma (30-80 Hz) range is related to a variety of sensory and cognitive processes which are frequently impaired in schizophrenia. Auditory steady-state response at 40-Hz (40-Hz ASSR) is utilized as an index of gamma activity and is proposed as a biomarker of schizophrenia. Nevertheless, the link between ASSRs and cognitive functions is not clear. This study explores a possible relationship between the performance on cognitive tasks and the 40-Hz ASSRs in a controlled uniform sample of young healthy males, as age and sex may have complex influence on ASSRs. Twenty-eight young healthy male volunteers participated (mean age ± SD 25.8±3.3) in the study. The 40-Hz click trains (500 ms) were presented 150 times with an inter-stimulus interval set at 700-1000 ms. The phase-locking index (PLI) and event-related power perturbation (ERSP) of the ASSR were calculated in the 200-500 ms latency range, which corresponds to the steady part of the response. The Psychology Experiment Building Language (PEBL) task battery was used to assess five cognitive subdomains: the Choice response time task, the Stroop test, the Tower of London test, the Lexical decision task and the Semantic categorisation task. Pearson's correlation coefficients were calculated to access the relationships; no multiple-test correction was applied as the tests were explorative in nature. A significant positive correlation was observed for the late-latency gamma and the mean number of steps in the Tower of London task reflecting planning and problem-solving abilities. These findings support the concept that 40-Hz ASSR might highlight top-down mechanisms which are related to cognitive functioning. Therefore, 40-Hz ASSRs can be used to explore the relationship between cognitive functioning and neurophysiological indices of brain activity.

Intra-individual reaction time variability and response preparation: an EEG study.

To behave more efficiently the human brain must anticipate future events with different probabilities and prepare appropriate responses. Previous studies demonstrated that participants react faster to more probable stimuli. It has been shown that this effect in reaction time reduction is related to the response preparation process. However it is still unknown what the minimum difference in stimulus probabilities is that is sufficient to elicit response preparation as measured with the EEG. Intra-individual reaction time variability indicates the stability of an individual's response performance and provides useful information about cognitive functioning. It's use has become prevalent in recent clinical studies. In order to extend understanding of cognitive and neural mechanisms of response stability we hypothesized that intra-individual reaction time variability relates to the response preparation process. Specifically, we hypothesized that response preparation to more probable stimuli would result in not only faster reaction time but also in a reduction of response variability. To verify this hypothesis, we tested 14 healthy subjects using reaction time and EEG as dependent measures. Two different stimuli with probabilities of 33.3% and 66.6% were assigned to two counterbalanced responses. The results of our study showed that stimulus probabilities of 66.6% and 33.3% were sufficient to elicit response preparation. Our data also revealed that response preparation to more probable stimuli speeds RT and reduces RT variability.