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by Rhawn Joseph, Nancy Forrest, Denise Fiducia, *Peter Como & *Jerome Siegel,
ABSTRACT
The relationships among levels of activity, responsiveness, exploration, and cortical arousal were assessed in a group of similarly reared male rats from a strain that was highly inbred to maximize genetic homogeneity. In Experiment 1, 22 subjects were tested in a complex, compartmentalized open field (i.e., a closed field), and those falling approximately 1 SD above or below the group activity mean (eight were eliminated) were designated as high- or low-active, implanted with electrodes, and tested electrophysiologically to ascertain the level of cortical arousal as determined via measurements of visually evoked potential afterdischarge amplitude. High-active subjects demonstrated significantly lower afterdischarge amplitude, indicating that behavioral arousal may be indexed by a readily quantifiable electrophysiological measure. A second group of 14 rats (Experiment 2) was tested and retested after 45 days in the closed field, establishing that high- or low-behavioral responsiveness is a stable characteristic. Subjects then received 2 days' exposure to one of two dissimilar compartments of an exploratory apparatus and were tested to determine amount of time spent in the familiar vs. novel compartments. High-active rats were found to demonstrate significantly shorter initial response latencies. However, no other differences were found. These rats were next tested in a completely open field. No significant activity differences were discovered. These findings show that a high level of arousal as a response to a highly complex environment or intense stimulation is not related to generalized activity elicited in a low-complexity environment (e.g., the open field). These findings also indicate that similarly reared rats may be differently influenced by novel, complex, or intense stimuli, such that some subjects become highly responsive and cortically aroused, whereas others respond with low levels of behavioral and cortical activation. The findings are discussed in terms of cortical and subcortical mechanisms mediating arousal.
INTRODUCTION
The factors contributing to individual differences in activity, exploration, and cortical arousal are not clearly understood. Behavioral, hormonal, electrophysiological, and neuroanatomical studies of a variety of species have suggested that differences in individual responsiveness are linked to differential rearing conditions, gender, genetic factors, and structural or functional differences in the excitability of the nervous system (Buchsbaum 1974; Como,Joseph, Fiducia, Siegel, & Lukas, 1979; Fleming, Rhodes, Wilson, & Shearer, 1973; Joseph, 1979; Joseph & Casagrande, 1978, 1980; Joseph & Gallagher, 1980; Joseph, Hess, & Birecree, 1978; Konrad & Bagshaw, 1970; Lukas & Siegel,1977b; Zuckerman, Murtaugh, & Siegel, 1974). The purpose of the present study was to assess the relationships among activity, behavioral responsiveness, and cortical arousal as measured by visually evoked potentials in a group of similarly reared, same-sex rats from a strain highly inbred to maximize genetic homogeneity.
In a number of studies, it has been demonstrated that the visually evoked potential (VEP)afterdischarge (AD) is a behaviorally sensitive form of EEG cortical synchrony that is dependent upon recurrent excitatory-inhibitory activity in the dorsal lateral geniculate nucleus and modulating influences of the thalamus, limbic system, and reticular activating system (RAS) (Bigler, 1975; Fleming et al., 1973; Klingbern, 1971; Knispel & Siegel, 1972; Lukas & Siegel, 1977a, 1977b; Schwartzbaum, 1975). For example, animals in a state of relaxed wakefulness (Klingbern, 1971)or rat strains that respond with low levels of behavioral activation (Fleming et al., 1973) show cortical synchronous EEG activity, as well as high-amplitude VEP ADS (Shearer & Creel, 1978), whereas rat strains that are characteristically highly active have a comparatively lower amplitude low-voltage fast EEG. Moreover, low-voltage fast EEG produced by activation of the RAS greatly dampens AD amplitude, whereas the AD is optimally produced during low levels of RAS activity (Fleming et al.,1973; Schwartzbaum, 1975). These findings indicate, therefore, that the amplitude of the VEP AD may be viewed as an index of cortical and behavioral arousal.
To establish whether individual differences in behavioral responsiveness of an otherwise homogeneous population of rats are related to cortical arousal (Experiment 1), subjects were tested in a complex closed-field apparatus (Joseph & Gallagher, 1980), were classified as high- or low-active, and were implanted with chronic indwelling electrodes, and the relationship between behavior and VEP AD amplitude was ascertained. To establish whether behavioral responsiveness is a stable trait(Experiment 2), a second group of subjects were tested, then retested after 45 days in the closed field.
To determine whether behavioral responsiveness is an interactive function of the individual and environment, or a stable characteristic expressed similarly across environments regardless of stimulus intensity, novelty, or complexity, these subjects were also tested in an apparatus designed to assess exploratory behavior and in a neutral, lower complexity, open-field environment.
EXPERIMENT 1
Method
Subjects. Twenty two male Delaware-Wistar rats born to six females bred in this laboratory were weaned at 25 days of age, placed in two large (48.5x40x20.5cm) standard-rack suspended cages for 20 days, then randomly separated into four large rearing cages (five to six subjects in each) until 70 days of age, at which time they were placed individually in standard-rack cages (40x23x20.5 cm). At the onset of the behavioral and electrophysiological tests, the subjects were 90 and 120 days of age, respectively. All the subjects were maintained on ad-lib food and water in a colony room with a reversed 12-h light/dark cycle and were tested during the dark phase.
Apparatus. To measure activity, a compartmentalized open field, referred to as a closed field and similar to that described by Joseph and Gallagher (1980), was employed. Briefly, the apparatus (93x82.5cm) consisted of one startbox (43x18.5cm), a 2-cm wire-mesh floor, marked into 10.5-cm squares, and maze-like alleyways of wooden barrier board. Illumination during behavioral tests was provided by a single 15-W red light suspended 2m directly above the field, and extraneous sound was masked with 85-90-dB white noise (BRS/LVE audio generator).
For conducting the electrophysiological study, the subjects were tested in a small (60x40cm) chamber lined with reflecting aluminum panels. The visual potential was elicited by a Grass PSI photostimulator flashtube enclosed in a sound-insulated wooden box with a frosted .5-cm Plexiglas cover on the front to provide even diffusion of light. The flashtube was placed in the chamber, 15 cm away from the subject. VEPs were amplified with a Grass P511 preamplifier, recorded on a Sanborn FM tape recorder (Model 3971B), and averaged by a Nuclear Chicago data retrieval computer (Model 7100), and the VEP averages were written out on a Mosley X-Y plotter (Model 7590).
Procedure. Prior to the onset of behavioral testing, all the subjects were briefly handled for four consecutive days to reduce cage-emergence stress and handling influences (Joseph, 1979). The subjects were habituated to the testing room 10 min before each test and were placed in a startbox, and their emergence latencies and square crossings were tabulated according to previously described criteria (Joseph et al., 1978). The subjects were tested for 10min/day for four consecutive days. Observers were hidden from view throughout. The subjects were distinguished as being either high- or low-active, depending on their tendency to consistently fall 1 SD above or below the daily square-crossing activity means. Eight rats were then eliminated, and the remaining subjects were coded so that all further assessment proceeded blindly.
The subjects were anesthetized with injections of Ketaset and chloral hydrate and were implanted with stainless steel screw electrodes, placed 2mm anterior to lambda and 3 mm lateral to the midline (Area 17), 3 mm posterior to lambda (cerebella ground electrode), and 7 mm anterior to bregma (reference electrode). All the subjects were permitted 7 days of recovery.
Evoked Potential Analysis. All rats were wrapped in a cloth harness and restrained, leaving only their heads exposed. After approximately 3 min of habituation, the subjects were placed in the testing chamber directly facing the flash unit. To assess for group differences in AD amplitude as a function of stimulus intensity, five intensities of light flash were each presented 30 times at a rate of 1 flash/5 sec, with 20sec elapsing before the onset of each intensity series. The intensities in foot candles were 5, 17, 55,155, and 370 (as measured by an Alphametrics 1010 photometer placed 15 cm in front of the flash unit). Order of intensity presentation was determined randomly and held constant for all the subjects. The amplitude of the first peak of the AD was computed and averaged for reach of the five intensities, using 400 data points over a 500-msec analysis interval. The first component of the AD was found to fall approximately 135 msec (P3-N3) after sweep onset (see Figure 1B). Similar findings have been reported elsewhere (Como et al., 1979; Shearer & Creel, 1978).
Results
Closed-Field Activity. A 2 by 4 analysis of variance (ANOVA) was performed on group scores (high- vs. low-active) across testing days, and it was established that the remaining 14 subjects demonstrated significantly different amounts of behavioral responsiveness in the closed field [F(1, 12)=28.34, p<.001].
VEP Amplitudes. A clear and highly significant difference in AD amplitude between high- and low-active rats was discovered [F(1,12)=12.158, p<.004], demonstrating that the highly responsive subjects maintained significantly lower amplitude across all intensities as compared with the behaviorally low-active rats. Figure 1 illustrates a typical EP and AD in a high-active rat (1A) and a low-active rat (1B) to the same intensity light flash.
Table 1 presents, for each rat, the mean activity score in the closed field across 4 days and the amplitude of the computer-averaged afterdischarge (P3-N3) for each of the five flash intensities.
The relationships of AD amplitudes and behavioral activity levels are graphically displayed in Figure 2. The slopes of AD amplitudes for both the high- and low-active rats show a trend toward reduction as a function of flash intensity, but these slopes are statistically non-significant. It may be that this trend is due to an arousal effect with high-intensity light flashes or is related to EP reducing, which we have reported in cats (Lukas & Siegel, 1977b).
Discussion
The results clearly demonstrate that individual and group differences in behavioral responsiveness to complex, novel, and intense forms of stimuli are correlated with cortical activation, as indicated by the amplitude of the VEP afterdischarge. Rats responding with high levels of behavioral activation exhibit low-amplitude ADs when stimulated with various intensities of light flashes, whereas rats demonstrating low behavioral responsiveness respond to light-flash stimulation with high-amplitude Ads and thus demonstrate lower levels of cortical activation. These findings indicate that low-active subjects possibly have a lower threshold for activation of cortical inhibition, as mediated via ascending reticular influences (Fuster, 1961; Orem & Feeney, 1971) or through intracortical activity (Dell, Bonvallet, & Hugelin, 1961; Demetrescu, & Tosif, 1965; Steriade, 1968).
Although it could be argued that high active rats are in fact responding with significantly higher levels of exploratory behavior, and the VEP AD components are actually measuring cortical processing of environmental cues, it must be cautioned that the behavioral factors measured were dependent upon activity and responsiveness to complex and intense forms of stimulation, variables that are often only weakly linked to exploratory behavior (Joseph & Gallagher, 1980). As pointed out by Joseph and Gallagher, such behavior is often indicative of tendencies to over respond. It is noteworthy that, once aroused, neither the high- nor low-active subjects significantly increased their cortical arousal level when they were exposed to the intense light flashes, suggesting that the low-active rats respond with significantly lower levels of cortical activation than do high-active subjects, regardless of the stimulus parameters. To clarify these issues, Experiment 2 was performed to determine if differential levels of behavioral activation in a closed-field environment reflect differences in novelty seeking (exploratory behavior) or simply differences in reactivity.
EXPERIMENT 2
Method
Subjects. Fourteen male Delaware-Wistar rats born to four females bred in this laboratory were weaned, placed in two large rearing cages at 25 days of age, and, at 100 days of age, were assigned individually to single standard-rack suspended cages. The subjects were approximately 180 days of age at the onset of testing. All rats were maintained on ad-lib food and water throughout the experiment in a colony room with a reversed 12-h light/dark cycle and were tested during the dark phase.
Apparatus. To measure behavioral responsiveness, the closed field employed in Experiment 1 was used. To assess preferences for familiar surroundings or for novelty (exploratory behavior), an apparatus similar to that described by Turpin (1977) was employed. Briefly, the apparatus was a 76x15x25 cm two-chamber wooden box, partially divided in the center by a wooden partition, with a 2-cm wire-mesh floor. The walls were flat gray, with either 2-cm horizontal or vertical black stripes. The effect of environmental stimuli on activity level was further assessed by testing all the subjects in a complexity-free, neutral environment simple open field (78x78x34cm), the floor of which (2-cm wire mesh) was divided into 10.5-cm squares.
Procedure. Behavioral responsiveness was measured in a manner identical to that described in Experiment 1, with the exception that, after the first 4-day test series, all the subjects were retested after 45 days for an additional 4-day period. To assess novelty seeking, the subjects were categorized as high- or low-active, based on their behavioral responsiveness scores, and were assigned randomly to a habituation condition in which they were placed into one-half of the exploratory apparatus (familiarity conditioning). The subjects were habituated twice a day—15min/session, with 3 h between each—for 2 days prior to testing. The subjects were also habituated for 10min immediately prior to testing, which comprised one 10-min session/day on two consecutive days. At the beginning of each test session, the subjects were placed at the center portion of the exploratory apparatus, and the latency to first movement was scored, the initial compartment preference was determined (entering either the familiar or novel compartment), separate shuttles between compartments were tabulated, and the amount of time spent in each compartment was computed.
Ten days after completion of the exploratory testing the subjects were assessed for activity elicited in the open field for 4 days, 10min/session. Open-field testing procedures were identical to those employed in the closed field.
All the subjects were tested during their dark cycle, using red-light illumination, except during preference (exploratory) testing, in which 30-W white-light illumination was provided 2 m directly above the apparatus. White noise (80-90 dB) was employed to mask extraneous sound throughout.
Results
The findings of this experiment are summarized in Table 2.
Closed-Field Activity. A 2 by 2 by 4 ANOVA was computed for groups (high-vs. low-active), test series (first 4 days vs. last 4), and closed-field behavior across all testing days. As in Experiment 1, the activity differences between groups were highly significant and were maintained across the four test sessions [F(1,12)=30.149, p<.001], as well as during the first [F(1,12)=38.78, p<.0001] and second tests [F(1,12)=5.36, p<.05].
Novelty Seeking. A 2 by 2 by 2 ANOVA was performed across high- and low-active groups, habituation conditions, and the following dependent variables: movement latency, initial preference, shuttles between compartments, and total time spent in each. A significant main effect was found for movement latency across testing days [F(1,12)=5.05, p<.05], such that high-active rats demonstrated a shorter response latency than did low-active subjects. No other significant differences were found.
Open-field activity. A 2 by 4 ANOVA was performed on all open-field behavior. No significant differences were found between groups.
Discussion
As demonstrated in Experiment 2, tendencies to respond with high levels of behavioral activation and arousal are dependent upon the stimulus parameters of the testing environment (e.g., complexity, intensity, novelty). Hence, in a neutral, relatively low-arousal environment, the behavior of high- and low-active rats is indistinguishable. However, these same subjects, when placed in the more complex closed field (compartmentalized open field), responded with high or low levels of behavioral activity and continued to do so when retested after 45 days. Although it could be argued that high-active rats are comparatively more exploratory, it is curious that there were no signs of habituation when they were retested in the closed field. Moreover, when provided with the opportunity to “explore” a novel compartment (vs. a familiar environment), no group differences were found. Since the stimulus parameters of the “exploratory” apparatus differed only in regard to horizontal or vertical position of wall stripes, it is likely that the compartment was not complex enough to elicit differential responding. Nevertheless, it is interesting to not that high-active rats were initially more responsive, demonstrating the quickest movement latencies when first placed in the center of the exploratory apparatus.
The significant difference in response latency, the failure to find activity differences in the open field, and the behavioral responsiveness that results from placement in a highly novel, complex environment suggests that high-active rats, although not constantly functioning at high levels of arousal, tend to become highly aroused and over responsive when exposed to complex and intense forms of stimulation.
The behavioral and electrophysiological results lend themselves to the suggestion that this tendency to over respond may be due to a failure to initiate cortical inhibition of ascending reticular and thalamic activity or to possible differences in cortical-subcortical structure and function, particularly in the frontal cortex region.
These suggestions are in part supported by the similarities of the behavior of high-active rats to the behavior of rats with frontal pole lesions (Como et al., 1980) and to animals reared in an impoverished environment (Joseph & Gallagher, 1980; Konrad & Bagshaw, 1970). Interestingly, impoverished rearing conditions have been shown to decrease dendritic density in the frontal regions (Walsh, Cummins, Budtz-Olsen, & Torok, 1972). This is significant in that the frontal cortex mediates motor output (Luria, 1973), exerts inhibitory influences on the reticular activating system (Lineberry & Siegel, 1971), receives terminal projections from the secondary association cortex of all sensory modalities (Jones & Powell, 1970), and thus mediates and organizes behavior in response to the sensory environment (Luria, 1973; Nauta, 1972). Hence, high levels of arousal and over responsivenes may result from a lowered stimulus threshold, as well as from a failure to integrate incoming sensory messages with motor output due to frontal-lobe dysfunction. In a complex environment, there is thus excessive cortical arousal, significant motor overflow, and, as demonstrated in deprived animals (Joseph & Gallagher, 1980), possibly learning deficits resulting from an inability to successfully integrate and selectively respond to complex environment stimuli.
Indeed, the frontal neocortex is "interlocked" with the limbic system, striatum, and the primary and secondary receiving areas via converging and reciprocal connections. In humans, the frontal lobes also receives verbal and ideational impulses transmitted from the multi-modality associational areas including Wernicke's receptive speech area and the multi-modal assimilation area in the inferior parietal lobule. It is thus able to act at all levels of information analysis.
Indeed, the frontal lobe receives input from and maintains extensie interconnections with the primary, seconday, and territiary/assimilation receiving areas, as well as the thalamus. (Pribram et al., 1953; Siegel et al., 1977), a major relay nucleus involved in the gating and filtering of information destined for the neocortex (Skinner & Yingling, 1977; Yingling & Skinner, 1977).
The medial magnocellular dorsal nucleus of the thalamus appears to exert modulating influences on information reception and processing as well as limbic arousal, and in this manner the frontal lobes are also able to act to modulate activity in widespread areas of the brain, the limbic system and cortical receiving areas in particular.
The medial portion of the magnocellular dorsal medial thalamic (MDMT) nucleus (like the orbital region) receives fibers from the reticular formation and amygdala (Chi, 1970; Krettek & Price, 1974; Siegel et al. 1977). However, this portion of the dorsal medial thalamus appears to be subject to orbital control (Joseph, unpublished). Indeed, the orbital region via it's interconnections with all three regions (i.e. reticular formation, limbic system, MDMT), is able to exert a considerable degree of influence on the interactions which take place in these nuclei, including control over various forms of limbic, behavioral and emotional arousal.
For example, electrical stimulation of the orbital area can cause a hungry animal to stop eating, walk away from its dish, lie down, and even fall into slow-wave synchronized sleep (Lineberry & Siegel, 1971). It can inhibit monosynaptic spinal reflexes (Clemente et al., 1966; Sauerland et al., 1967), as well as reduce and inhibit arousal throughout the neocortex (Lineberry & Siegel, 1971), limbic system (Steriade, 1964), including the reticular formation (Lineberry & Siegel, 1971; Siegel & Wang, 1974). Indeed, the orbital region appears to exert hierarchical control over the MDMT, reticular formation, limbic and autonomic nervous system, thus mediating generalized arousal throughout the neuroaxis. As pertaining to emotional arousal, it has also been postulated that the orbital area exerts a major influences on the experience of anxiety, including the development of ulcers (Freeman & Watts, 1942).
The inferior and lateral convexity appears to be highly involved in the inhibition of behavior and the ability to withhold or delay responses, which in turn is in part a function of its involvement in controlling neocortical perceptual activity and arousal (Como et., al, 1979). Hence, electrophysiological analysis of cellular activity within the lateral convexity indicates that many neurons alter their discharge rates when a subject is required to wait before responding to a signal. Yet others increase of decrease their activity as the time interval between the onset of the delay and the release of the response increases. The majority of these delay neurons are found within the inferior convexity. However, a number of neurons in the superior convexity show similar properties.
Similarly, high frequency electrical stimulation of the lateral and inferior convexity has been shown to disrupt the ability to inhibit, delay, and withold responses (Goldman et al. 1970; Gross & Weiskrantz, 1964; Stamm & Rosen, 1969), whereas low frequency stimulation actually improves performance on delayed response tasks and enhances behavioral inhibition (Wilcott, 1974, 1977). Interestingly, electrical stimulation of the right frontal region, as compared to the left, more greatly disrupts delayed response performance.
Conversely, when the lateral and inferior convexity are damaged there results a consistent disturbance across tasks requiring the withholding and delay of a response (Brutkowski et al. 1963; Gross & Weiskrantz, 1964; Mishkin & Pribram, 1956; Stepien & Stamm, 1970). That is, animal and human subjects become disinhibited and impulsive --disturbances which in turn effect all aspects of behavior. Patients may spontaneously speak or make comments "without thinking", and act on sudden impulses without regard for consequences.
Frontal-Thalamic Interactions
With the exception of olfaction, ll sensory impulses are first transferred to the thalamus before being transmitted to the primary auditory, visual, and somesthetic receiving areas. From the primary zones this information is sent to 3 separate major locations: to the immediately adjacent sensory association area, back to the thalamus, and to the motor cortex of the frontal lobes.
The motor area then relays this information to the lateral convexity which simultaneously receives fiber projections from the sensory association areas (Jones et al. 1978; Jones & Powell, 1970; Pandya & Kuypers, 1969) and the inferior parietal lobule. Hence, the frontal cortex and right and left lateral convexity are "interlocked" with the posterior sensory areas via converging and reciprocal connections with the first, second, and third level of modality specific analysis, including the multimodal associational integration performed by the inferior parietal lobule. The frontal lobes, therefore able to sample activity within all cortical sensory/association regions at all levels of information analysis.
FRONTAL-THALAMIC CONTROL OVER NEOCORTICAL ACTIVITY
The role of the lateral convexity is not limited to sampling, but also involves regulation of information flow to and within the neocortex. This is accomplished, in part, via projections linking the frontal lobes with the dorsal medial thalamic nucleus--a structure which participates in the transfer of information to the neocortex and which display neuroplasticity (Jones & Pons, 1998).
Fibers passing to and from the thalamus and the cortical sensory receiving areas give off collaterals to the reticular thalamic nucleus--which in addition sends fibers which envelop and innervate most of the other thalamic nuclei (Scheibel & Scheibel, 1966; Updyke, 1975). The reticular thalamus maintains reccurent inhibitory interconnections with other thalamic neuron and acts to synchronize and selectively gate transmission from the thalamus to the neocortex and continually samples thalamic-cortical activity (Skinner & Yingling, 1977; Yingling & Skinner, 1977).
The reticular thalamus is controlled by the lateral convexity of the frontal lobes, and the lateral portion of the dorsal medial thalamus with which it maintains dense interconnections (Skinner & Yingling, 1977; Yingling & Skinner, 1977). The convexity and lateral dorsal medial nucleus (LDM) are also richly interconnected and together exert significant steering influences on the reticular thalamus. That is, the lateral frontal convexity appears to exert specific influences on the LDM so as to promote or diminish the flow of information to the cortex and thus modulate specific perceptual and cognitive activities occuring within the neocortex --activity which it is simultaneously sampling. This is in contrast to the orbital region with its connections to the reticular formation and the medial magnocellular segment of the dorsal medial thalamus, and its influences on generalized arousal and limbic activation/inhibition.
To recapitulate, the lateral frontal system is able to influence cognitive/perceptual cortical functioning via the sampling of activity occurring throughout the neocortex at all levels of informational analysis, and via its modulating influences on the lateral portion of the dorsal medial and reticular thalamic nuclei. The lateral frontal region is thus able to act at any stage of processing, from initial reception to motor expression so as to facilitate or inhibit further analysis, selectively acting to determine exactly what type of processing occurs throughut the neocortex.
Via integration and inhibitory action and through its neocortical and thalamic links the lateral convexity it is able to coordinate interactions between various regions of the neuroaxis so as to organize, mobilize, and direct overall cortical and behavioral activity and to minimize conflicting demands, impulses, distractions and/or the processing of irrelevant information.
When damaged, depending on the site (e.g. inferior vs superior convexity) or laterality of the lesion, there can result behavioral disinhibition, flooding of the sensory association areas with irrelevant information, hyperreactively, distractability, memory loss, impulsiveness, and/or apathy, reduced motor-expressive activities (e.g. speech arrest), and sensory neglect (Como et al. 1979). Similar disturbances can result when the dorsal medial nucleus or the bi-directional pathways linking the thalamus and frontal lobe are severed (Skinner & Yingling, 1977).
Hence, in summary, the oribtal region exerts modulating influences on subcortical and geralized limbic arousal. By contrast, the lateral convexity of the frontal lobes are "interlocked" with the the sensory receiving areas (Jones et al. 1978; Jones and Powell 1970; Pandya and Kuypers 1969) and maintains rich interconnections with the reticular and dorsal medial nucleus of the thalamus (Skinner and Yingling 1977; Yingling and Skinner 1977) which relays sensory impressions to the neocortex. The lateral frontal lobes, therefore are able to sample perceptual input as it is received in the thalamus, and thus prior to and after it has been transferred to the neocortical receiving areas. Through its interconnections with the primary and association areas, the frontal lobes can also censor, inhibit, and thus control the processing of this data, and in this manner can control attention as well as facilitate or inhibit further analysis and thus information processing throughout the neocortex. These frontal capabilities include information storage and retrieval at the neocortical level; i.e. memory.
CONCLUSION The frontal lobes serve as the "Senior Executive" of the brain and personality, acting to process, integrate, inhibit, assimilate, and remember perceptions and impulses received from the limbic system, striatum, temporal lobes, and neocortical sensory receiving areas. Moreover, through the assimilation and fusion of perceptual, volitional, cognitive, and emotional processes, the frontal lobes engages in decision making and goal formation, modulates and shapes character and personality and directs attention, maintains concentration, and participates in information storage and memory retrieval. Hence, when damaged, attention, concentration and other cognitive functions, including learning and memory, become disrupted due to excessive arousal and disinhibition.
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