Multichannel near-infrared spectroscopy in depression and schizophrenia: cognitive brain activation study.

BACKGROUND: Recent developments in near-infrared spectroscopy (NIRS) have enabled the noninvasive clarification of brain functions in psychiatric disorders with measurement of hemoglobin concentrations as cerebral blood volume. METHODS: Ten patients with depression, 13 patients with schizophrenia, and 16 age- and gender-matched healthy control subjects participated in the study after giving consent. The relative concentrations of oxyhemoglobin [oxyHb] were measured with frontal and temporal probes every.1 sec during word fluency and unilateral finger tapping tasks, with two 24-channel NIRS machines. RESULTS: The [oxyHb] increase patterns during the word fluency task varied among the three groups, although their task performances were similar: the depression group was characterized by a smaller [oxyHb] increase during the first half of the task period and the schizophrenic group by a small trough of [oxyHb] at the start of the task period and [oxyHb] re-increase in the posttask period. [OxyHb] increases during the finger-tapping task were rather larger in the patient groups than in the control group. CONCLUSIONS: The characteristic time courses of [oxyHb] changes in the frontal lobe were elucidated for depression and schizophrenia. Near-infrared spectroscopy, with its noninvasiveness and high time resolution, can be a useful tool for research and clinical purposes in psychiatry.     

Hypofrontality in panic disorder and major depressive disorder assessed by multi-channel near-infrared spectroscopy

Background: Panic disorder is a common and debilitating psychiatric disease; yet, the neurobiology of this disorder is not fully understood. Deficits in the prefrontal inhibitory control over hyperactivity of the anxiety‐related neural circuit are implicated in the pathophysiological core of panic disorder. The aims of this study were to investigate whether panic disorder reveals frontal lobe dysfunction while performing the word fluency test by using multi‐channel near‐infrared spectroscopy and to compare the findings in panic disorder with those in major depressive disorder. Methods: Twenty‐one patients with panic disorder, 17 patients with major depressive disorder, and 24 healthy control subjects participated in the study. Results: Both patients with panic disorder and with major depressive disorder showed similarly attenuated increases in oxy‐hemoglobin during the word fluency test in the bilateral frontal regions, when compared to healthy control participants. Hypofrontality in panic disorder and major depressive disorder was most prominent in the left medial inferior frontal lobe. Conclusions: This study clarified that hypofrontality in panic disorder is evident even with neutral stimuli of little emotional load. Depression and Anxiety 25, 2008. © 2008 Wiley‐Liss, Inc.     

Alterations in prefrontal cortical activity in the course of treatment for late-life depression as assessed on near-infrared spectroscopy

Aim:  To evaluate the severity of depression by measuring alterations in prefrontal cortical activity associated with mood disorders, as assessed on near-infrared spectroscopy.
Methods:  Ten of 27 subjects hospitalized for late-life depression from May 2006 to June 2007, were examined. In these 10 subjects changes in hemoglobin concentration were measured on near-infrared spectroscopy during two types of the rock, paper, scissors game as the cognitive tasks affecting prefrontal cortical activity on 2 days, including 1 day on which depressive symptoms had slightly improved due to treatment, and then on another day >4 weeks later. Severity of depression and cognitive impairment were also simultaneously assessed.
Results:  The change in oxygenated hemoglobin concentration during a difficult task (intentional loss task) was significantly larger than that during an easy task (try to win task) on the left side (left, P  = 0.010; right, P  = 0.059). On the left side there was a significant negative correlation between the ratio of oxygenated hemoglobin measurements on the second day to those on the first day, and the severity of depression on the second day (left, P  = 0.012; right, P  = 0.090). Thus, the more left prefrontal cortical activity tended to increase, the fewer depressive symptoms tended to be present on the second day of testing.
Conclusions:  Measuring of alterations in prefrontal cortical activity associated with mood disorders, as assessed on near-infrared spectroscopy, is feasible in subjects with depression.     

Cerebral autoregulation in the microvasculature measured with near-infrared spectroscopy

Cerebral autoregulation (CA) is the mechanism that allows the brain to maintain a stable blood flow despite changes in blood pressure. Dynamic CA can be quantified based on continuous measurements of systemic mean arterial pressure (MAP) and global cerebral blood flow. Here, we show that dynamic CA can be quantified also from local measurements that are sensitive to the microvasculature. We used near-infrared spectroscopy (NIRS) to measure temporal changes in oxy- and deoxy-hemoglobin concentrations in the prefrontal cortex of 11 human subjects. A novel hemodynamic model translates those changes into changes of cerebral blood volume and blood flow. The interplay between them is described by transfer function analysis, specifically by a high-pass filter whose cutoff frequency describes the autoregulation efficiency. We have used pneumatic thigh cuffs to induce MAP perturbation by a fast release during rest and during hyperventilation, which is known to enhance autoregulation. Based on our model, we found that the autoregulation cutoff frequency increased during hyperventilation in comparison to normal breathing in 10 out of 11 subjects, indicating a greater autoregulation efficiency. We have shown that autoregulation can reliably be measured noninvasively in the microvasculature, opening up the possibility of localized CA monitoring with NIRS.     

Activation of the prefrontal cortex during the Trail-Making Test detected with multichannel near-infrared spectroscopy

The Trail-Making Test (TMT) is a neuropsychological test for evaluating executive function, and the TMT Part B reflects more complex cognitive processes including cognitive set shifting. The prefrontal cortex (PFC) is thought to be involved in these cognitive processes. The purpose of the present paper was to investigate PFC activation during performance of the TMT Part A and Part B using multichannel near-infrared spectroscopy (NIRS). Subjects were 41 healthy right-handed volunteers. The hemodynamic changes in the PFC during the TMT were measured on a 22-channel NIRS machine. The subjects had a greater increase of oxygenated hemoglobin ([oxyHb]) during the TMT Part B than during Part A in the PFC. Twenty-seven out of the 41 subjects had a bilateral increase of [oxyHb] in the PFC during Part B according to laterality index. NIRS detected activation in the PFC during the performance of the TMT Part B and this PFC activation may reflect executive functions including cognitive set shifting involved in the TMT Part B.     

Regional cerebral blood flow abnormalities in late-life depression:Relation to refractoriness and chronification

Abstract We examined patterns of regional cerebral blood flow (rCBF) abnormalities in 18 patients with major depressive disorder in late life using single photon emission computed tomography (SPECT) and (^99mTc-hexamethyl-propylenamine oxime (^99mTc-HMPAO). Compared with 13 age-matched controls, relative rCBF was significantly decreased bilaterally in the anterior cingulate gyrus, the prefrontal cortex, the temporal cortex, the parietal cortex, the hippocampus and the caudate nucleus. However, it was not correlated with the severity of depression or global cognitive dysfunction. In 10 patients with a prolonged depressive episode or prolonged residual symptoms (the refractory subgroup), robust and extensive decreases in rCBF were found compared with controls and the rCBF decreased significantly in the anterior cingulate gyrus and the prefrontal cortex compared with that in the non-refractory subgroup. In the non-refractory subgroup, rCBF decreased significandy in the caudate nucleus and tended to decrease in the anterior cingulate gyrus compared with controls. These findings indicate that dysfunction of the limbic system, the cerebral association cortex and the caudate nucleus may be implicated in late-life depression and that robust and extensive hypoperfusion, especially in the anterior cingulate and the prefrontal regions, may relate to refractoriness or chronification of depression.     

Changes in cerebral blood flow after acetazolamide: an experimental study comparing near-infrared spectroscopy and SPECT

Background and purpose:  It is important to find a reliable and bedside method, which can estimate the cerebral blood flow (CBF) of patients in clinical settings. Estimation of CBF by calculating a blood flow index (BFI) using continuous wave near-infrared spectroscopy (CW-NIRS) and indocyanine green (ICG) as an iv tracer has been proposed to be a feasible and promising method. To validate if the BFI method can detect relative changes in CBF we compared data with the established method ¹³³Xenon single photon emission computer tomography (¹³³Xe-SPECT).
Methods:  Ten healthy subjects were investigated before and after a bolus of acetazolamide. NIRS data were obtained using a multi source detector separation configuration in order to assess a corrected BFI (BFI_corr) value, which attempts to eliminate contamination of skin blood flow.
Results:  Data obtained showed no significant correlation between CBF changes measured by ¹³³Xe-SPECT and BFI_corr (0.133, P  =   0.732). After acetazolamide, a 49% increase in CBF was detected using the ¹³³Xe-SPECT method, whereas no changes in any ICG variables were observed after acetazolamide.
Conclusion:  The study shows that it is not possible to obtain reliable BFI data, which reflect changes in CBF after acetazolamide infusion, using the CW-NIRS and ICG method.     

Functional near-infrared spectroscopy during the verbal fluency task of English-Speaking adults with mood disorders: A preliminary study

Functional near-infrared spectroscopy (fNIRS) provides a direct and objective assessment of cerebral cortex function. It may be used to determine neurophysiological differences between psychiatric disorders with overlapping symptoms, such as major depressive disorder (MDD) and bipolar disorder (BD). Therefore, this preliminary study aimed to compare fNIRS signals during the verbal fluency task (VFT) of English-speaking healthy controls (HC), patients with MDD and patients with BD. Fifteen HCs, 15 patients with MDD and 15 patients with BD were recruited. Groups were matched for age, gender, ethnicity and education. Relative oxy-haemoglobin and deoxy-haemoglobin changes in the frontotemporal cortex was monitored with a 52-channel fNIRS system. Integral values of the frontal and temporal regions were derived as a measure cortical haemodynamic response magnitude. Both patient groups had lower frontal and temporal region integral values than HCs, and patients with MDD had lower frontal region integral value than patients with BD. Moreover, patients could be differentiated from HCs using the frontal and temporal integral values, and patient groups could be differentiated using the frontal region integral values. VFT performance, clinical history and symptom severity were not associated with integral values. These results suggest that prefrontal cortex haemodynamic dysfunction occurs in mood disorders, and it is more extensive in MDD than BD. The fNIRS-VFT paradigm may be a potential tool for differentiating MDD from BD in clinical settings, and these findings need to be verified in a larger sample of English-speaking patients with mood disorders.     

Changes in regional cerebral blood flow abnormalities in late-life depression following response to electroconvulsive therapy

The impact of electroconvulsive therapy (ECT) on the regional cerebral blood flow (rCBF) abnormalities in late-life depression is still unknown and the clinical significance of these findings in late-life depression has not been fully discussed. Using single photon emission computed tomography (SPECT) with 99mTc-hexamethylpropylene amine oxime (99mTc-HMPAO), we examined the changes of rCBF patterns in nine late-life patients with major depressive episodes before and following response to ECT compared with nine age- and sex-matched healthy volunteers. Statistical comparisons were made on both region-of-interest (ROI) and voxel-by-voxel bases. In ROI-based analyses, a mean rCBF was significantly decreased in the patients before ECT compared with the control, significantly increased (normalized) in the patients 2 weeks after ECT compared with that before ECT, and still increased in the patients 12 weeks after ECT compared with that before ECT. In voxel-by-voxel analyses, a significant rCBF reduction was found in the bilateral pre- and subcallosal anterior cingulate cortex, the bilateral caudal orbitofrontal cortex, the right insular cortex and the right posterior middle frontal gyrus in patients before ECT compared with the control, and similar rCBF patterns were shown at 2 weeks and 12 weeks after ECT. We propose the hypothesis that a mean rCBF reduction may have a state-related property while persistent anterior paralimbic hypoperfusion may have a trait-like property, which relates to the relapse vulnerability as well as a tendency toward medication failure and illness chronicity in late-life depression.     

Evaluation of cerebral activity in the prefrontal cortex in mood [affective] disorders during animal-assisted therapy (AAT) by near-infrared spectroscopy (NIRS): A pilot study

Objective. Previous studies have shown the possibility that animal-assisted therapy (AAT) is useful for promoting the recovery of a patient's psychological, social, and physiological aspect. As a pilot study, we measured the effect that AAT had on cerebral activity using near-infrared spectroscopy (NIRS), and examined whether or not NIRS be used to evaluate the effect of AAT biologically and objectively. Methods. Two patients with mood [affective] disorders and a healthy subject participated in this study. We performed two AAT and the verbal fluency task (VFT). Results. The NIRS signal during AAT showed great [oxy-Hb] increases in most of the prefrontal cortex (PFC) in the two patients. When the NIRS pattern during AAT was compared with that during VFT, greater or lesser differences were observed between them in all subjects. Conclusion. The present study suggested that AAT possibly causes biological and physiological changes in the PFC, and that AAT is useful for inducing the activity of the PFC in patients with depression who have generally been said to exhibit low cerebral activity in the PFC. In addition, the possibility was also suggested that the effect of AAT can be evaluated using NIRS physiologically and objectively.     

Application of functional near-infrared spectroscopy to explore the neural mechanism of transcranial direct current stimulation for post-stroke depression

ABSTRACT

Objectives: We investigated the neural mechanism of transcranial direct current stimulation (tDCS) in the treatment of post-stroke depression (PSD) using functional near-infrared spectroscopy (fNIRS).

Methods: Twenty-six patients with PSD were randomly divided into an experimental group receiving tDCS and a control group receiving sham stimulation. The anode and cathode were placed on the left and right dorsolateral prefrontal cortex (PFC). Patients underwent fNIRS before and after treatment, combined with an emotional face sex judgment task and a ‘1-back’ working memory task to assess reaction times and relative concentration changes of oxyhemoglobin (Oxy-Hb) in the PFC.

Results: Reaction times for faces showing positive emotions decreased after treatment in the experimental group (P < 0.05). For faces showing negative emotions, relative Oxy-Hb concentration changes in the PFC were higher after treatment (P < 0.05), but there was no significant difference between the experimental and the control group. Reaction times during the working memory task in the experimental group were shorter after treatment (P < 0.05), and there was a significant difference between the groups (P < 0.05). Relative Oxy-Hb concentration changes in the left PFC were significantly higher after treatment in the experimental group (P < 0.05), and concentration changes in the right PFC after treatment were significantly higher in the experimental than in the control group (P < 0.05).

Discussion: tDCS may improve the processing of negative emotions and working memory in patients with PSD by enhancing aerobic metabolism in the PFC, thereby improving depressive symptoms.     

Cerebral hemodynamics measured with simultaneous PET and near-infrared spectroscopy in humans

Near-infrared spectroscopy (NIRS) enables continuous non-invasive quantification of blood and tissue oxygenation, and may be useful for quantification of cerebral blood volume (CBV) changes. In this study, changes in cerebral oxy- and deoxyhemoglobin were compared to corresponding changes in CBF and CBV as measured by positron emission tomography (PET). Furthermore, the results were compared using a physiological model of cerebral oxygenation. In five healthy volunteers changes in CBF were induced in a randomized order by hyperventilation or inhalation of 6% CO(2). Arterial content of O(2) and CO(2) was measured several times during each scanning. Changes in deoxyhemoglobin (deltaHb), oxyhemoglobin (deltaHbO(2)) and total hemoglobin (deltaHb(tot)) were continuously recorded with NIRS equipment. CBF and CBV was also determined in MRI-coregistered PET-slices in regions determined by the placement of the two optodes, as localized from the transmission scan. The PET-measurements showed an average CBV of 5.5+/-0.74 ml 100 g(-1) in normoventilation, with an increase of 29% during hypercapnia, whereas no significant changes were seen during hyperventilation. CBF was 51+/-10 in normoventilation, increased by 37% during 6% CO(2) and decreased by 25% during hyperventilation. NIRS showed significant increases in oxygenation during hypercapnia, and a trend towards decreases during hyperventilation. Changes in CBV measured with both techniques were significantly correlated to CO(2) levels. However, deltaCBV(NIRS) was much smaller than deltaCBV(PET), and measured NIRS parameters smaller than those predicted from the model. It is concluded that while qualitatively correct, NIRS measurements of CBV should be used with caution when quantitative results are needed.     

Increase of frontal cerebral blood volume during transcranial magnetic stimulation in depression is related to treatment effectiveness: A pilot study with near‐infrared spectroscopy

Aim

Alterations of cerebral blood flow have been reported in studies of depression treated by transcranial magnetic stimulation (TMS). However, the relation between these changes in activity during stimulation and the effectiveness of TMS is not known. The aim of this study was to determine whether changes in frontal cerebral blood volume measured as frontal hemoglobin concentration (fHbC) during TMS are correlated with clinical outcomes of treatment.

Methods

Fifteen drug‐resistant patients with depression underwent a standard treatment regimen of TMS to the left dorsolateral prefrontal cortex. We recorded fHbC during stimulation at the start and end of the TMS treatment series using near‐infrared spectroscopy. Symptom severity was determined using the Montgomery–Åsberg Depression Rating Scale.

Results

At the start of the TMS series, fHbC increased during stimulation in a majority of patients with no relation to symptom severity. However, at the end of the series, fHbC increase during stimulation was negatively correlated with the Montgomery–Åsberg Depression Rating Scale score and positively with the score reduction. Patients showing a decreasing response of fHbC during TMS at the end of the series experienced less clinical improvement.

Conclusion

These results suggest that the maintenance of frontal activation during stimulation in the course of TMS series is related to the effectiveness in the treatment of depression. Measurement of fHbC during stimulation is informative in the clinical use of TMS.

     

帕金森病患者额叶磁共振波谱的改变及其临床意义

目的研究帕金森病(PD)患者额叶磁共振波谱(1H-MRS)的改变及其临床意义。方法对36例PD患者(Hoehn-YahrⅠ级14例、Ⅱ级8例、Ⅲ级8例、Ⅳ级6例)和20名年龄匹配的正常对照者的双侧额叶进行1H-MRS检测,对比分析不同Hoehn-Yahr级别PD患者与正常对照组的额叶N-乙酰基天门冬氨酸(NAA)/肌酸复合物(Cr)和含胆碱化合物(Cho)/Cr值的变化。结果Hoehn-YahrⅢ级和Ⅳ级PD患者双侧额叶的NAA/Cr值显著低于正常对照组(P<0.005,P<0.01),Cho/Cr值显著高于正常对照者(均P<0.005);Hoehn-YahrⅠ级和Ⅱ级PD患者双侧额叶的NAA/Cr和Cho/Cr值与正常对照组差异无统计学意义。结论Hoehn-YahrⅢ级和Ⅳ级PD患者额叶1H-MRS有明显异常。提示1H-MRS有助于PD病情的评估。     

Reduced frontopolar activation during verbal fluency task associated with poor social functioning in late‐onset major depression: Multi‐channel near‐infrared spectroscopy study

Aim: Functional neuroimaging studies to date have indicated prefrontal dysfunction in late‐onset major depression (LOD). The relationships between prefrontal dysfunction and clinical characteristics including social functioning, however, have been unclear. The objective of the present study was to evaluate prefrontal hemodynamic response related to an executive task in LOD and to assess the relationship between activation in the prefrontal regions and clinical characteristics including social functioning. Methods: Twenty‐four subjects with LOD and 30 age‐ and gender‐matched healthy subjects were recruited for the present study. Hemoglobin concentration changes in the prefrontal and superior temporal cortical surface area were measured during verbal fluency task (VFT) using 52‐channel near‐infrared spectroscopy (NIRS), which enables real‐time monitoring of cerebral blood volume (CBV) in the cortical surface area. Results: The two groups had a distinct spatiotemporal pattern of oxy‐hemoglobin concentration change; LOD patients had less activation in a broad area covering both prefrontal and superior temporal cortices than healthy controls. In addition, reduced activation of the frontopolar region had a significant positive correlation with lower self‐assessment of social functioning scores in the patient group. Conclusion: Reduced frontopolar cortical activation was associated with social functioning impairment in patients with LOD, and NIRS may be an efficient clinical tool for monitoring these characteristics.     

Partitioning of physiological noise signals in the brain with concurrent near-infrared spectroscopy and fMRI

The blood–oxygen level dependent (BOLD) signals measured by functional magnetic resonance imaging (fMRI) are contaminated with noise from various physiological processes, such as spontaneous low-frequency oscillations (LFOs), respiration, and cardiac pulsation. These processes are coupled to the BOLD signal by different mechanisms, and represent variations with very different frequency content; however, because of the low sampling rate of fMRI, these signals are generally not separable by frequency, as the cardiac and respiratory waveforms alias into the LFO band. In this study, we investigated the spatial and temporal characteristics of the individual noise processes by conducting concurrent near-infrared spectroscopy (NIRS) and fMRI studies on six subjects during a resting state acquisition. Three time series corresponding to LFO, respiration, and cardiac pulsation were extracted by frequency from the NIRS signal (which has sufficient temporal resolution to critically sample the cardiac waveform) and used as regressors in a BOLD fMRI analysis. Our results suggest that LFO and cardiac signals modulate the BOLD signal independently through the circulatory system. The spatiotemporal evolution of the LFO signal in the BOLD data correlates with the global cerebral blood flow. Near-infrared spectroscopy can be used to partition these contributing factors and independently determine their contribution to the BOLD signal.     

Effects of movement music therapy with a percussion instrument on physical and frontal lobe function in older adults with mild cognitive impairment: a randomized controlled trial

ABSTRACT

Objectives: We tested the hypothesis that performing a rhythmic physical task accompanied by a cognitive task, such as multitask movement music therapy (MMT) involving repetitive rhythmic movement with a musical instrument (the Naruko clapper), may improve pre-frontal cortex (PFC) function and cognitive performance.

Method: Forty-five older adult participants with MCI (74.62 ± 5.05 years) participated in this randomized, controlled, single-blind intervention trial. 35 were assigned to the MMT group and 10 to the control STT group. Before and after the 12-week exercise program, we administered six physical function tests, the Frontal Assessment Battery (FAB), and measured relative oxyhemoglobin concentrations using 45-multichannel functional near-infrared spectroscopy as a reflection of hemodynamic responses in the PFC.

Results: We observed significant improvements in FAB scores only in the MMT group. Cerebral blood flow (CBF) in the PFC during the exercise was significantly increased in the MMT group compared with the STT group. The CBF increase was significantly correlated among various channels in the MMT group.

Conclusions: The MMT program appeared to stimulate the PFC and improve cognitive performance in our older adult participants with MCI, suggesting that the repetitive, rhythmic movements of MMT can activate the prefrontal area in older adults.

Trial registration: Clinical Trial Registry Numbers: R000026130, UMIN000022671 (2016/06/08) [(University Hospital Medical Information Network (UMIN) Center] retrospectively registered.     

Correlation between special brain area and blood perfusion in patients with cerebral infarction at convalescent period

BACKGROUND: Presently, clinic memory scale is used to evaluate learning memory ability in most studies, and the influence of difference in measurement condition of individuals exists. OBJECTIVE: To study the correlation between regional cerebral blood flow (rCBF) perfusion and learning memory function in special brain regions of patients with cerebral infarction at convalescent period, and to try to find out a method which can quantitatively evaluate learning ability. DESIGN: Case observation, and correlation analysis. SETTINGS: Shandong Institute for Behavioral Medicine; the Affiliated Hospital of Jining Medical College. PARTICIPANTS: Totally 70 patients with cerebral infarction admitted to Department of Neurology, Jining Medical College between January 2004 and December 2005 were involved. The involved patients, 58 male and 12 female, were averaged （52±3）years, and they were all right handed. They all met the diagnosis criteria instituted by the Fourth National Conference on Cerebrovascular Disease, and were confirmed as cerebral infarction by skull CT or MRI. Informed consents of detected items were obtained from all the patients and relatives. METHODS: When the patients were at convalescent period, their learning and memory ability were measured with " clinic memory scale (set A)". The 18 patients whose total mark over 100 were regarded as good learning memory function group; The 23 cases whose total mark less than 70 were regarded as poor learning memory function group. RCBF of hippocampus, nucleus amygdalae, temporal cortex and prefrontal lobe of patients between two groups were measured and compared by single photon emission computed tomography (SPECT). The total scores of the 18 good learning memory patients and 23 poor learning memory patients were taken as dependent variable Y, and their rCBFs of hippocampus, nucleus amygdale, temporal cortex and prefrontal lobe respectively as independent variable X for linear correlation analysis. MAIN OUTCOME MEASURES: Correlation of rCBF in different brain regions and learning memory ability in patients with cerebral infarction. RESULTS: ① The rCBF of hippocampus, nucleus amygdale, temportal cortex and prefrontal cortex of good learning memory function group were significantly higher than those of poor learning memory function group (P < 0.05). ②In the good learning memory function group, rCBF of hippocampus, nucleus amygdale, temportal cortex and prefrontal cortex were significantly positively correlated with memory scale scores（r = 0.961, 0.926, 0.954, 0.907, P < 0.05）, and also in the poor learning memory function group （r = 0.979, 0.976, 0.991, 0.953, P < 0.05）. CONCLUSION: The rCBF of hippocampus, nucleus amygdale, temportal cortex and prefrontal cortex of patients with cerebral infarction are significantly positively correlated with memory scale scores. Predicting learning memory ability of patients by quantitative determination of rCBF provides a quantitative and objective method for evaluating learning memory ability.