Neural response to the second stimulus associated with poor speed discrimination performance in schizophrenia

Visual motion processing is compromised in schizophrenia (SZ), but it is uncertain what neural deviations account for their motion analysis abnormalities. Neural activations were measured with dense-array electroencephalography while 14 medicated SZ and 14 healthy persons performed a paired-stimuli forced choice speed discrimination task. SZ had (a) worse-at-speed discrimination, replicating previous findings, (b) normal early extrastriate neural activity (N1) to both motion stimuli, (c) reduced later extrastriate activity (P2) specifically to the second stimulus, and (d) following P2, an enhanced later N2 over parietal cortex. Stronger P2 and N2 responses were associated with better speed discrimination performance across groups. These findings indicate that the neural correlates of poor motion analysis in SZ may not be an early visual analysis abnormality but a problem with efficient use of speed information later in cognitive processing.     

Recovery of function after brain damage: Differences in aged rats?

Age at the time of brain injury is generally considered an important determinant in recovery of function. The implication is that older individuals show less recovery. Existing data challenge this common notion, but suggest differential effects of brain damage in aged subjects. To assess these differences old rats were trained on a two-choice brightness discrimination, subjected to visual decortication, and retrained with nonreversed or reversed reinforcement contingencies. A significant reversal impairment established that sparing of function in aged rats was similar to that in adult rats. However, a significant reversal X brightness interaction suggested that the progress of recovery of function in aged rats is influenced not only by what is spared but also by whether the expression of what is spared is consistent with or antagonistic to competing innate response biases.     

Effects of physostigmine and scopolamine on operant brightness discrimination in the rat

Performance in an operant brightness discrimination was facilitated through the mid-range of training by injections of 0.3 mg/kg physostigmine. Performance was facilitated, compared to saline injected controls, due to lower response rates during S^Δ while S^D response rates were not affected. Injection of 0.5 mg/kg scopolamine suppressed both S^D and S^Δ response rates proportionally and thus did not affect discrimination performance as reflected in the discrimination ratio. The facilitation of discrimination performance produced by physostigmine was interpreted as due to facilitation of inhibitory precesses and as consistent with the hypothesis of a central cholinergic inhibitory mechanism.     

Impairment and recovery of visual functions after bilateral lesions of superior colliculus

Adult, male hooded rats were tested on a six-choice jumping stand apparatus designed to study their ability to perform visually guided orientation movements with a brightness discrimination task. Upon reaching criterion, the rats suffered either one- or two-stage, bilateral electrolytic lesions of the superior colliculi and then, after a brief recovery period, were retested for their ability to retain the preoperatively learned task and, in addition, perform a more difficult task. Although both brain damaged groups evidenced an impairment in comparison to sham-operated controls, the rats with two-stage lesions were less disabled than their simultaneously operated counterparts.     

Avoidance and brightness discrimination conditioning in genetically different lines of rats

Rats from an albino stock were selected for high (HAS) and low (LAS) avoidance scores measured in a shuttle-box. Learning performance of male rats was compared in three different tests: the shuttle-box, the pole jumping-box, and the Y-chamber. It was shown that rats of the HAS line more rapidly acquired conditioned avoidance in the shuttle-box experiment and the pole-jumping experiment than LAS, whereas we could not detect any significant differences in brightness discrimination. In the open field test rats of the HAS line were more active in comparison to LAS's, measured in terms of higher ambulation scores. In conclusion, it is verified that the shuttle-box performance as well as pole-jumping performance is highly determined by the emotional status of the animals and, moreover, that avoidance learning is based on mechanisms other than brightness discrimination learning.     

Deficient brightness discrimination in hooded but not albino rats given neocortical ablations

Hooded and albino rats with lesions of the neucortex overlying hippocampus and normal rats of both strains were trained in an operant discrimination. Though the normal groups did not differ from one another and the neocortically lesioned albinos did not differ from the unlesioned rats, when compared to the other groups the hooded group was found to be deficient in the acquisition of the task. A greater amount of cell loss and gliosis was observed in the thalamus of the hooded rats.     

Discrimination learning and reversal following electrolytic lesions of the median raphe nucleus

The current study examined the effects of electrolytic median raphe lesions on the performance of several T-maze discrimination tasks. Raphe lesions were found to impair the reversal, but not the acquisition, of a learned position habit, but to be without effect on either the acquisition or reversal of simultaneous brightness discrimination task. Rats with raphe damage were severely impaired in the acquisition of either a successive brightness discrimination task or of a delayed spatial alternation task. These results are similar to those which have been reported after limbic damage, and support the view that the paramedian midbrain tegmentum may play an important role in the functioning of limbic structures.     

Hyperthymic temperament and rapid reaction time in brightness preference

Background

It is well-known that Type A behavior pattern is characterized by hard-driving, competitive behavior and time urgency. Also, people with hyperthymic temperament are known to have high energy levels and are full of plans. It is therefore hypothesized that hyperthymic temperament is associated with rapid processing and fast reaction time in making decisions.

Methods

Using data from our previous experimental studies (N=58) examining brightness judgment and brightness preference, reaction time (RT) was investigated in relation to hyperthymic temperament scores and fMRI signal changes of the left inferior orbitofrontal cortex during brightness judgment.

Results

RT for brightness judgment was significantly shorter than RT for brightness preference. Significant associations were found between RT for brightness preference and hyperthymic temperament scores, and RT for brightness preference and fMRI signal changes of the left inferior orbitofrontal cortex whilst performing brightness preference task. Multiple regression analysis revealed that RT for brightness preference task was significantly and negatively associated with hyperthymic temperament scores, and significantly and positively associated with fMRI signal changes of the left inferior orbitofrontal cortex.

Limitations

It is uncertain whether the findings of RT (around 1 s) can be extrapolated to routine life (around 24 h) and whether RT for brightness preference can be generalized to a variety of daily activities.

Conclusions

The present findings suggest that hyperthymic temperament is associated with rapid processing. Further studies are required to overcome the above limitations.     

Projection patterns of surviving neurons in the dorsal lateral geniculate nucleus following discrete lesions of striate cortex: implications for residual vision

Summary In four monkeys with long-standing partial ablation of the striate cortex pellets of horseradish peroxidase were placed in either the striate cortex immediately adjacent to the ablation, or in the extrastriate cortex of the ventral prelunate gyrus, i.e. in visual area V4. We examined the dorsal lateral geniculate nucleus to see whether surviving neurons, within the region that shows retrograde degeneration as a result of the cortical lesion, project to remaining striate cortex and/or to extrastriate cortex. Neurons labelled from extrastriate cortex were found throughout the degenerated region, whereas neurons labelled from striate cortex were confined to the border between the normal and degenerated region of the nucleus. This shows that isolated neurons found within the degenerated region survive striate cortex damage because they project to an extrastriate visual area, and not because their terminals depart from the otherwise strict topographic representation of the lateral geniculate nucleus on to striate cortex.     

Brightness discrimination learning in a Skinner box in prenatally X-irradiated rats

Male MP 1 albino rats were exposed to X-irradiation in utero at a single dose of 200 R on Day 17 of gestation. The light-dark discrimination training in a Skinner box was continued until the animals attained a learning criterion of 0.80 correct response ratio for 3 consecutive days. Although during the unreinforced baseline sessions the total number of bar pressings in the irradiated animals was superior to that in the controls, performance between the control and the irradiated animals did not differ significantly in (a) the number of training days required to attain the learning criterion, (b) the total number of days on which the animals produced a correct response ratio more than 0.80, and (c) the number of consecutive days during which the correct response ratio was more than 0.75. The results obtained suggest that the irradiated animals were able to discriminate in brightness cues as well, or nearly as well, as the controls. The cortical-subcortical system mediating brightness discrimination in the irradiated animals was discussed.     

Retroactive memory of a visual discrimination task in the rat: role of temporal-entorhinal cortices and their connections

Summary It has previously been shown that the temporal and entorhinal cortices may be critically involved in memory. In Experiment 1, rats with either damage to the temporal cortex (TC), lateral entorhinal cortex (LEC), or the medial entorhinal cortex (MEC) were tested for retention of a preoperatively acquired simultaneous brightness discrimination task. TC and LEC lesions impaired retention, whereas MEC lesions were without mnemonic effect. In Experiment 2, rats with either disruptions of the anterior neural connections of TC (TC/Ant), posterior connections of TC (TC/Post), or conjoint disruptions (Ant/Post) were tested for retention of the visual discrimination task. TC/Ant and Post/Ant lesions resulted in relatively mild, but significant memory impairment, whereas a profound effect was seen after TC/Post lesions. The results are discussed in terms of a very important role for LEC and its connections with TC in mnemonic function.     

Hippocampal and amygdaloid involvement in working memory for nonspatial stimuli

Hippocampal lesions in rats lead to an impairment of performance in spatial delayed conditional discriminations. The effect of such lesions on nonspatial tasks is controversial. In monkeys, both the hippocampus and the amygdala are involved in nonspatial delayed conditional discriminations. The effect of amygdaloid lesions in rats on this type of task has not been studied. To clarify the role of hippocampus and amygdala in a cue-relevant/space-irrelevant delayed conditional discrimination, rats were trained on a delayed match-to-sample task with visual and tactile cues as discriminative stimuli. Rats were then given one of five lesions: control, complete fimbria-fornix, partial fimbria-fornix, complete amygdala, or partial amygdala. Amygdaloid lesions, partial or complete, did not impair choice accuracy. Fimbria-fornix lesions did impair choice accuracy, and the magnitude and duration of the impairment was a function of the size of the lesion. Partial fimbria-fornix lesions produced a slight impairment that disappeared with continued testing. Complete fimbria-fornix lesions produced chance performance throughout postoperative testing. These results indicate that the fimbria-fornix, but not the amygdala, is involved in nonspatial delayed match-to-sample.     

Evidence of state dependent learning of brightness discrimination in hypothermic mice

Shock-elicited escape behavior of C57Bl mice in a brightness discrimination task was examined to investigate the effects of hypothermia on acquisition and reversal. Neither acquisition nor reversal was impaired by 7 degrees C or 13 degrees C decreases in central body temperature when body temperature remained at those levels throughout testing. However, body temperature changes from acquisition to reversal were accompanied by memory deficits during reversal if acquisition occurred at body temperature decreased by 13 degrees and reversal occurred at normal body temperature or body temperature decreased by 7 degrees and reversal at body temperature decreased by 13 degrees. This finding suggests the occurrence of a state dependent discrimination response: an instance of asymmetrical dissociation. In addition, during acquisition, latency of the escape response was longer in hypothermic animals than in controls, and should be interpreted as a performance deficit, rather than failure or delayed rate of learning. Depressed intertrial activity also was observed in hypothermic animals.     

Prefrontal modulation of visual processing in humans

Single neuron, evoked potential and metabolic techniques show that attention influences visual processing in extrastriate cortex. We provide anatomical, electrophysiological and behavioral evidence that prefrontal cortex regulates neuronal activity in extrastriate cortex during visual discrimination. Event-related potentials (ERPs) were recorded during a visual detection task in patients with damage in dorsolateral prefrontal cortex. Prefrontal damage reduced neuronal activity in extrastriate cortex of the lesioned hemisphere. These electrophysiological abnormalities, beginning 125 ms after stimulation and lasting for another 500 ms, were accompanied by behavioral deficits in detection ability in the contralesional hemifield. The results provide evidence for intrahemispheric prefrontal modulation of visual processing.     

Brain regions involved in spatial frequency discrimination: evidence from fMRI

The cortical areas underlying successive spatial-frequency discrimination were explored using functional magnetic resonance imaging (fMRI). In a steady-state, block-design paradigm, 12 subjects viewed a single fixation cross during a rest period, followed by an activation period consisting of the presentation of horizontal (distractors) and vertical (targets) sinewave gratings. Two tasks were performed: in the control task, subjects pressed a button after the second vertical grating was presented within each trial; in the discrimination task, subjects decided which target grating had the higher spatial frequency. Post-processing consisted of off-line image registration to correct for head motion, spatial and temporal smoothing, and cross-correlation between each voxel time course and a phase-shifted stimulus time profile. The results indicate that striate, extrastriate, parietal, and prefrontal areas show significant BOLD (blood oxygen level dependent) effects during both discrimination and control tasks, with consistently higher activity levels in the discrimination task.     

The neurophysiological correlates of colour and brightness contrast in lateral geniculate neurons

Summary The colour of an object is changed by surround colours so that the perceived colour is shifted in a direction complementary to the surround colour. To investigate the physiological mechanism underlying this phenomenon, we recorded from 260 neurons in the parvo-cellular lateral geniculate nucleus (P-LGN) of anaesthetized monkeys (Macaca fascicularis), and measured their responses to 1.0–2.0° diameter spots of equiluminant light of various spectral composition, centered over their receptive field (spectral response function, SRF). Five classes of colour opponent neurons and two groups of light inhibited cells were distinguished following the classification proposed by Creutzfeldt et al. (1979). In each cell we repeated the SRF measurement while an outer surround (inner diameter 5°, outer diameter 20°) was continuously illuminated with blue (452 nm) or red (664 nm) light of the same luminance as the center spots. The 1.0–1.5° gap between the center and the surround was illuminated with a dim white background light (0.5–1cd/m²). During blue surround illumination, neurons with an excitatory input from S-or M-cones (narrowand wide-band/short-wavelength sensitive cells, NSand WS-cells, respectively) showed a strong attenuation of responses to blue and green center spots, while their maintained discharge rate (MDR) increased. During red surround illumination the on-minus-off-responses of NS- and WS-cells showed a clear increment. L-cone excited WL-cells (wide-band/long-wavelength sensitive) showed a decrement of on-responses to red, yellow and green center spots during red surround illumination and, in the majority, also an increment of MDR. The response attenuation of narrow-band/long-wavelength sensitive (NL)-cellls was more variable, but their on-minus-off-responses were also clearly reduced in the average during red surrounds. Blue surround illumination affected WL-cell responses little and less consistently than those of NL-cells, but often broadened the SRF also in the WL-cells towards shorter wavelengths. The M-cone excited and S-cone suppressed WM-cells were strongly suppressed by blue but only little affected by red surround illumination. The changes of spectral responsiveness came out clearly in the group averages of the different cell classes, but snowed some variation between individual cells in each group. The zero-crossing wavelengths derived from on-minus-off-responses were also characteristically shifted towards wavelengths complementary to those of the surround. The direction of changes of spectral responsiveness of P-LGN-cells are thus consistent with psychophysical colour contrast and colour induction effects which imply that light of one spectral region in the surround reduces the contribution of light from that same spectral region in the (broad band or composite) object colour. Surrounds of any colour also decrease the brightness of a central coloured or achromatic light (darkness induction). We calculated the population response of P-LGN-units by summing the activity of all WS-, WM- and WL-cells and subtracting that of all NS- and NL-cells. The SRF of this population response closely resembled the spectral brightness function for equiluminous lights rather than the photopic luminosity function. With red or blue surrounds, this population SRF was lowered nearly parallel across the whole spectrum to about 0.7 of the amplitude of the control. In a psychophysical test on 4 observers we estimated the darkness induction of an equiluminous surround in a stimulus arrangement identical to the neurophysiological experiment, and found a brightness reduction for white, blue, green and red center stimuli to 0.5–0.7 of the brightness values without surround. This indicates that the neurophysiological results may be directly related to perception, and that P-LGN-cells not only signal for chroma but also for brightness, but in different combinations. The results indicate that both an additive (direct excitation or suppression of activity) and a multiplicative mechanism (change of gain control) must be involved in brightness and colour contrast perception. As mechanisms for the surround effects horizontal cell interactions appear not to be sufficient, and a direct adaptive effect on receptors feeding positive or negative (opponent) signals into the ganglion cells receptive fields by straylight from the surround must be seriously considered. This will be examined in the following companion paper. The results indicate that changes of spectral and brightness responses in a colour contrast situation sufficient to explain corresponding changes in perception are found already in geniculate neurons and their retinal afferents. This applies to mechanisms for colour constancy as well in as much as they are related to colour contrast.This paper is dedicated to the memory of Prof. Günter Baumgartner, Zürich. The material was first presented on the occasion of his 65^th birthday in 1989     

Differences in Y-maze retention of rats: Selection according to open field activity

Adult male Wistar rats of a heterogeneous outbred population were selected according to their open field ambulation and classified into two groups: animals showing the most activity during the first 2 min (A, fast habituation), or after the first 2 min (B, delayed habituation) of a 10 min observation period. One week later these rats were tested for foot-shock motivated brightness discrimination learning and retention in a Y-maze. It was found that group A rats exhibited higher %-savings than group B rats, whereas their learning performance was not different. Thus, our results show that rats differing in their Y-maze retention ability can be selected on the basis of certain open field measures.     

Object discrimination by rats: The role of frontal and hippocampal systems in retention and reversal

The present experiment was designed to determine whether the reversal deficit in nonspatial discrimination tasks following frontal or hippocampal system damage was a result of the spatial components of those tasks, or a general reversal deficit. Rats were trained to choose between two objects based on the stimulus characteristics of the objects themselves; neither the absolute location of the objects in the test arena nor the position of the objects with respect to the rat accurately predicted the correct choice. Rats with either frontal cortex or fimbria-fornix lesions performed worse than controls in both postoperative retention and reversal of the object discrimination. The performance of rats with frontal cortex damage was impaired during the first two postoperative reversals; but not during subsequent reversals. The performance of rats with fornix lesions was impaired only on the first postoperative reversal. These data demonstrate that the nonspatial reversal impairment following damage to either the frontal cortical or hippocampal systems is the result of a general reversal deficit, and is not due to the spatial components of nonspatial tasks.     

Discrimination learning requiring different memory components in rats: age and neurochemical comparisons

The performances of young (8-9 months) and aged (22-24 months) male ACI rats were compared in a T-maze requiring two discriminations, each of which placed different demands on memory processing. A spatial discrimination in the stem of the T-maze required long-term reference memory; a discrete-trial, alternation discrimination in the arms of the T-maze required working memory. Following acquisition training in one maze, rats were also trained in a second maze at a different location in the room. The correct response in the stem of this maze was opposite to that in the first maze. In two experiments with slightly different pretraining procedures, similar results demonstrated that aged rats made more errors in all phases of maze training than did their young counterparts. The results suggest that all components of memory processing were affected equivalently because the age-related impairment was not selectively greater in any component of the task. In a third experiment, aged rats were unimpaired in the ability to perform in a T-maze task involving a brightness discrimination with intramaze cues. This result suggests that the age-related impairment in the two-component T-maze task was restricted to the cognitive demands of the task. Neurochemical analyses were performed to determine whether regional neurotransmitter synthetic enzyme activities could be used to identify neurochemical systems associated with performance in these tasks and with any age-related impairments observed. Choline acetyltransferase and glutamic acid decarboxylase were assayed as markers for cholinergic and GABAergic systems, respectively, in the hippocampi and the following cortical regions: frontal, sensorimotor, auditory, cingulate, occipital, and pyriform-perirhinal. A slight (8%) but significant age-related decline was observed in the activity of glutamic acid decarboxylase but not of choline acetyltransferase. Although the correlation between maze performance and regional enzyme activities generally supported several previous observations, the only significant correlation to emerge was between working memory performance and glutamic acid decarboxylase activity in the cingulate cortex.     

Hyperthymic temperament and brightness preference in healthy subjects: Further evidence for involvement of left inferior orbitofrontal cortex in hyperthymic temperament

Background

Hyperthymic temperament has been generally accepted as one of premorbid temperament of bipolar disorders. Although several studies indicate that subjects with hyperthymic temperament receive more illuminance, our recent study suggests that the threshold of brightness and darkness judgment is not different between more and less hyperthymic subjects, and that hyperthymic temperament may be associated with left inferior orbitofrontal cortex, which has been reported to be associated with bipolar disorder. Therefore, at the next stage, it can be hypothesized that hyperthymic subjects may prefer brightness (i.e., heliotropism) and thereby seek illuminance, and that percent signal changes of left inferior orbitofrontal cortex during the preference task may be associated with hyperthymic temperament scores.

Methods

We compared brightness preference and un-preference between more and less hyperthymic subjects, and investigated percent signal changes of left inferior orbitofrontal cortex during brightness preference judgment, brightness un-preference judgment, and control task by using functional Magnetic Resonance Imaging (fMRI).

Results

There were significant differences in brightness preference judgment and un-preference judgment, showing that more hyperthymic subjects preferred brighter illuminace levels and un-preferred darker illuminance levels than less hyperthymic subjects. Moreover, fMRI signal changes of left inferior orbitofrontal cortex was significantly and negatively associated with hyperthymic temperament scores.

Limitations

It is unknown why left but not right inferior orbitofrontal cortex was associated with hyperthymic temperament scores.

Conclusions

The present findings suggest that more hyperthymic subjects may prefer brightness and un-prefer darkness than less hyperthymic subjects (i.e., heliotropism), and reconfirm that hyperthymic temperament may be associated with left inferior orbitofrontal cortex, which have been reported to be associated with bipolar disorders.