Dissociation of item and order memory following parietal cortex lesions in the rat

Order information in working memory: an integrative review of evidence from brain and behavior

Evidence about memory for order information comes from a number of different methodologies: human cognition, patient studies, neuroimaging studies, and animal lesion and behavioral studies. The present article discusses (a) evidence that order and item memory are separable; (b) proposed mechanisms for order memory (interitem associations, direct codes, hierarchical codes, feature codes, and magnitude codes) and evidence for each; (c) evidence for the neural substrates of order memory from patient, neuroimaging, and animal lesion and single-cell recording studies; (d) barriers to integration between the disciplines; and (e) suggestions for better coordination of efforts between the different disciplines.

Broad band spectral EEG parameters correlated with different IQ measurements

The relationship of IQ (measured by WAIS and all its subscales) and EEG broad band spectral parameters were studied in 40 right-handed, male volunteers ranging in age from 20 to 25 years old. EEGs were recorded in 20 derivations during rest with eyes opened. The results obtained reveal positive and negative correlations with abundant frontal participation in all bands. Mean frequency data show a frequency shift in a very narrow range suggesting that more relations in narrow band could be achieved. These results highlight the need of psychological tests that measure more homogeneous abilities and finer measurement technique to reveal clearly explainable correlations and demonstrate that EEG recordings do reflect intellectual abilities.

Differential temporal evolution of post-training changes in regional brain glucose metabolism induced by repeated spatial discrimination training in mice: visualization of the memory consolidation process?

The present study analyses the effects of the stage of learning on the spatial patterns and time-course of [14C]glucose uptake in BALB/c mice brain regions produced by spatial discrimination training in an eight-arm radial maze. Our particular approach was designed to follow, during the post-training period, the level of functional activity in individual brain areas which may underlie the memory consolidation process. Regional mapping of relative [14C]glucose uptake was assessed at three post-training time intervals (5 min, 1 and 3 h) after either the first (Day 1), the fourth (Day 4) or the last (Day 9) daily training session of the discrimination task and compared with sham-conditioned animals placed in the same experimental environment. The results indicated that numerous subcortical and cortical brain regions exhibit metabolic alterations following the acquisition of the spatial discrimination task. These alterations, which were specifically related to learning since they did not appear in sham-conditioned animals, were functions both of the post-training interval studied and of the degree of mastery of the task. On Day 1, a progressive, time-dependent and sequential increase in labelling was found from subcortical (5 min post-training) to cortical regions (3 h post-training). On Day 4, a peak of cortical metabolic activation was identified at 1 h post-training. In contrast, on Day 9, maximum labelling was found 5 min post-training in all subcortical and cortical regions followed by a general monotonic decline at 1 and 3 h post-training. These findings, which show widely distributed changes of metabolic activity in the brain, are consistent with the hypothesis that learning involves distributed neural networks. The sequential activation from subcortical to cortical regions seems to indicate a general mechanism whose function would ultimately be to store cortical memory representations. The acquisition-dependent shifts in the patterns of post-training metabolic labelling observed as a function of task mastery may be taken to represent a visualization of the spatio-temporal evolution of the networks of brain structures actively engaged in the memory consolidation process. In particular, the present data suggest that the duration of post-acquisition memory processing is a function of the quantity of new information which has to be dealt with by the central nervous system.

Spatial deficits and hemispheric asymmetries in the rat following unilateral and bilateral lesions of posterior parietal or medial agranular cortex

Studies of spatial behavior in both the human and non-human primate have generally focused on the role of the posterior parietal and prefrontal cortices and have indicated that destruction of these regions produce allocentric and egocentric deficits, respectively. The present study examined the role of the rodent analogs of these regions, the posterior parietal (PPC) and medial agranular (AGm) cortices, in egocentric and allocentric spatial processing, and whether spatial processing in rodents is organized in a hemispatial and/or lateralized manner as has been found in the primate. Eighty male rats receiving either a unilateral or bilateral lesion of AGm or PPC were examined on an egocentric (adjacent arm) or an allocentric (cheeseboard) maze task. The results indicated that PPC and AGm have dissociable spatial functions. Bilateral AGm destruction resulted in egocentric spatial deficits, and unilateral AGm operates demonstrated an intermediate deficit. In contrast, bilateral PPC operates demonstrated a severe deficit in allocentric processing. In addition, there were lateralized differences in the performance of unilateral PPC operates. While right PPC lesions resulted in a significant deficit on the allocentric task, no such deficit was seen in left PPC operates. In addition, neither unilateral AGm nor unilateral PPC operates demonstrated a hemispatial impairment on either the egocentric or allocentric tasks.

Exploratory activity and response to a spatial change in rats with hippocampal or posterior parietal cortical lesions

Rats with bilateral lesions of posterior parietal cortex (PPC: Krieg's Area 7) or dorsal hippocampus (HIP) were compared with controls for their response to environmental change. In the first experiment, following subjects' exploration of a relatively homogeneous open-field environment, a stimulus-rat was introduced at a particular location beneath the glass floor. All groups selectively explored the location of the stimulus-rat, but only the control and PPC groups displayed habituation. On removal of the stimulus-rat, only the control group selectively re-explored the place where the stimulus-rat had been. A second experiment, similar to the first, used additional prominent visual cues beneath the floor. When the cues were spatially separate from the location of the stimulus-rat (Dissociated object condition), the same results were obtained as in the first experiment. When the additional cues were positioned close to the stimulus-rat location (Associated object condition), habituation occurred in all groups including the hippocampal group, and again the removal of the stimulus-rat resulted in a selective re-exploration of its former location in the control group only. However, a selective preference for staying at the stimulus-rat's previous location was found in PPC animals as in controls. Hippocampal rats failed to investigate the location of the missing stimulus in all conditions. The results confirm the role played by the hippocampus in spatial memory and suggest that the posterior parietal cortex is involved in the cognitive-demanding aspects of spatial encoding, particularly in environments that are poorly visually differentiated.

Spatial recognition and spatial order memory in patients with dementia of the Alzheimer's type

Patients diagnosed as having mild or moderate primary degenerative dementia of the Alzheimer's type (PDDAT), and normal elderly subjects were tested for spatial order and a spatial recognition memory. Results for spatial order memory indicated that compared to normal elderly subjects, patients with mild PDDAT showed an impaired memory only for the last serial positions. In contrast, with respect to spatial recognition memory, patients with mild PDDAT showed an impaired memory only for the early serial positions. Patients with moderate PDDAT were impaired on all serial positions for both spatial order and spatial recognition memory. Based on comparable deficit patterns seen in animals and patients with hippocampal and parietal cortex lesions, it is suggested that memory deficits displayed by PDDAT patients might be a function of underlying pathology in the hippocampus and parietal cortex.

Time-dependent sequential increases in [14C]2-deoxyglucose uptake in subcortical and cortical structures during memory consolidation of an operant training in mice

Previous results have suggested that memory processing may involve the sequential activation of subcortical and cortical structures. To study this phenomenon, we have examined the immediate (15 min) and delayed (220 min) metabolic changes produced in BALB/c mice by a partial training session in a bar-pressing appetitive task, using the [14C]-2-deoxyglucose (2-DG) relative glucose uptake method. These relative metabolic changes were compared to the ones produced in several control groups: untrained animals, sham-conditioned animals, overtrained animals, and animals forced to walk on a moving belt (immediate and delayed condition). Animals were given a single intrajugular injection (5 microCi) of 2-DG either 5 min before or 3 h (delayed condition) after the second training session. Forty minutes after the 2-DG injection, the animals were sacrificed and their brains processed for autoradiography. At the 15-min delay, a large 2-DG labeling increase was found in partially trained animals for various subcortical areas (septum, diagonal band, hippocampus, thalamus, and mammillary bodies) while a much smaller increase was found in four cortical areas (frontal, cingulate, parietal, and sensory motor cortices). At the 220-min delay, we observed a large 2-DG labeling increase in cortical (frontal, pyriform, and cingulate cortices) and subicular areas while a moderate 2-DG labeling increase was observed in entorhinal cortex and the diagonal band. These results show that, shortly after training, subcortical structures are preferentially activated while cortical structures are much less activated. Three hours later, at a time when retention performances have been shown to improve spontaneously in the same strain of mice and in the same task, cortical structures are highly activated.

Memory deficits following nucleus basalis magnocellularis lesions may be mediated through limbic, but not neocortical, targets

In order to test the contribution of the target areas of the nucleus basalis magnocellularis to the mediation of item and order recognition memory for spatial locations, one set of rats received lesions of the dorsolateral frontal cortex, parietal cortex, or basolateral amygdala after training in an order recognition memory task, whereas another set of animals received lesions of the nucleus basalis magnocellularis or basolateral amygdala in an item recognition memory task. Animals with basolateral amygdala lesions displayed a deficit for order recognition memory, but no deficit for item recognition memory, a pattern equivalent to that found for animals with nucleus basalis magnocellularis lesions. In contrast, animals with dorsolateral frontal cortex displayed no deficit, and animals with parietal cortex lesions displayed only a partial deficit for order recognition memory, results that differ from those found for animals with nucleus basalis magnocellularis lesions. It appears that the nucleus basalis magnocellularis influences item and order recognition memory for lists of spatial locations primarily through projections to limbic but not neocortical targets.