We evaluated the effects of DLPFC lesions (including both banks of the principal sulcus) in rhesus monkeys on tests of scene learning and strategy implementation that are severely impaired following crossed unilateral lesions of frontal cortex and inferotemporal cortex. 
Area 45A borders dorsally, in the proximity of the principal sulcus, with area 46 and, ventrally, with area 12.
Motor-symptomatic animals had decreases in beta2* and beta4* nAChR in the principal sulcus (40-60%), anterior cingulate sulcus (30-55%), and orbitofrontal cortex (30-41%), but not in the hippocampus, plus significant decreases in binding (70-80%) in the caudate and putamen.
MATERIALS AND METHODS: Eight adult male African green monkeys were treated with saline or phencyclidine (0.3 mg/kg BID x 14 days) and, after 8 days drug-free, perfused and fixed, and the principal sulcus was collected (Walker's area 46) for immunohistochemical analysis.
We reversibly inactivated portions of the principal sulcus in 2 monkeys trained to perform AS and RS tasks. Here we show that inactivation of a circumscribed area in the ventral bank of the principal sulcus induced a strong impairment of RS inhibition without affecting RS triggering. Our results are compatible with a partitioning of the principal sulcus into functional subregions, in which a well-delineated area is critically involved in RS suppression..
The cells projecting to the SEF and pre-SMA were mainly distributed in the upper and lower banks of the principal sulcus (area 46), with little overlap.
For each cortical domain, we show the anatomical position and extent of visuo-oculomotor activity, including evidence that the dorsolateral frontal activation, which includes the frontal eye field (on the anterior bank of the arcuate sulcus), extends anteriorly into posterior principal sulcus (area 46) and posteriorly into part of dorsal premotor cortex (area 6).
In contrast, there was no change in [ (125)I]alpha-btx binding in the brain regions thought to be involved in mediating the cognitive functions impaired in these monkeys (e.g., the hippocampus, areas 9/46D and 46D of the principal sulcus, and area 24c of the cingulate sulcus).
Both Statistical Parametric Mapping and regions of interest-based analyses revealed an increase of rCBF in the area surrounding the principal sulcus (PS), the superior convexity, the anterior bank of the arcuate sulcus (AS), the lateral orbitofrontal cortex (lOFC), the frontal pole (FP), the anterior cingulate cortex (ACC), the lateral bank of the intraparietal sulcus (lIPS) and the prestriate cortex.
The dorsorostral part of F7 (supplementary eye field, F7-SEF) was found to be a target of strong afferents from the frontal eye field (FEF), from the dorsolateral prefrontal regions located dorsally (DLPFd) and ventrally (DLPFv) to the principal sulcus and from cingulate areas 24a, 24b and 24c.
Spiking characteristics of neurons in the middle temporal (MT) area and the medial superior temporal (MST) area in the visual cortex of a monkey are compared with the ones in the principal sulcus (PS) area in the prefrontal cortex.
Three inferior prefrontal regions in the monkey receive afferents from somatosensory cortices: the orbitofrontal cortex (OFC), the ventral area of the principal sulcus, and the anterior frontal operculum.
Cells projecting to the ventral sector were distributed in the lower bank of the principal sulcus (PS).
When glutamate concentration was compared between the delayed alternation and sensory-guided tasks, difference was observed only in the dorsolateral prefrontal cortex, especially in the ventral lip area of the principal sulcus.
Its principal frontal corticocortical connections were with the prefrontal cortex in the shoulder above the principal sulcus and the cortex in the shoulder above the superior ramus of the arcuate sulcus (SAS), the area purported to contain the smooth eye movement-related frontal eye field (FEFsem) in the cebus monkey by other investigators.
Shape-selective neurons were located more anteriorly in the ventral bank of the principal sulcus and inferior convexity area, whereas location-selective neurons were more posteriorly. When muscimol was microinjected into the ventral bank of principal sulcus and inferior convexity area, the performance of both tasks was impaired.
Injection of multiple tracers into physiologically mapped regions AL, ML and CL of the auditory belt cortex revealed that anterior belt cortex was reciprocally connected with the frontal pole (area 10), rostral principal sulcus (area 46) and ventral prefrontal regions (areas 12 and 45), whereas the caudal belt was mainly connected with the caudal principal sulcus (area 46) and frontal eye fields (area 8a).
However, it appears that no study has investigated the direct relationship between the length of the principal sulcus and performance on a delay-response task. Therefore, this paper investigates the relationships between principal sulcus length and performance on delay-response tasks. However, to control for the effect of overall brain size on this relationship, cranial capacity is analyzed with both principal sulcus length and delay-response performance. Results support a consistent and significant correlation between principal sulcus length and performance on delayed-response tasks in a variety of Old World and New World monkeys. principal sulcus length is also significantly correlated with cranial capacity; however, cranial capacity is not significantly correlated with performance on delayed-response tasks. The results of this investigation provide a method for analyzing cranial capacity and working-memory abilities in select primates based on principal sulcus length, and may prove useful for interpreting endocasts in the primate fossil record..
To examine this issue, rhesus monkeys were chronically implanted with guide cannulae directed at the principal sulcus, medial prefrontal cortex, premotor cortex, and caudate nucleus. Clozapine produced significant and long-lasting increases in dopamine release in the principal sulcus, and to a lesser extent, in the caudate nucleus. Haloperidol did not produce a consistent effect on dopamine release in the principal sulcus, although it increased dopamine release in the caudate.
First, CPB injections label many neurons in dorsal prearcuate cortex in the region of the frontal eye field and neurons in dorsal prefrontal cortex of the principal sulcus, but few or no neurons in orbitofrontal cortex. Second, RPB injections label overlapping prearcuate and principal sulcus locations, as well as more rostral cortex of the principal sulcus, and several locations in orbitofrontal cortex. Third, STGr injections label locations in orbitofrontal cortex, some of which overlap those of RPB injections, but not prearcuate or principal sulcus locations. Fourth, injections in prearcuate and principal sulcus locations labeled by a CPB injection labeled neurons in CPB and RPB, with little involvement of the auditory belt and no involvement of the core.
Injections that included rostral and orbital prefrontal areas (10, 46 rostral, 12) labeled the rostral belt and parabelt most heavily, whereas injections including the caudal principal sulcus (area 46), periarcuate cortex (area 8a), and ventrolateral prefrontal cortex (area12vl) labeled the caudal belt and parabelt.
While labeling within the banks of the principal sulcus, the dorsal part of the arcuate concavity, and the banks of the upper arcuate limb were present in both 7a and MST-FST injected animals; in the latter cases, additional projections were found towards frontal regions including the dorsomedial frontal cortex and the posterior bank of the arcuate ventral limb.
In monkeys, a prefrontal cortical region important for spatial working memory lies in and around the principal sulcus, but in humans the location, and even the existence, of a region for spatial working memory is in dispute.
The increase appeared to reflect the working memory component of the task and was observed mainly in the lip areas of principal sulcus.
The predominant neural input to these two subregions originates in other cortical eye fields, including the supplementary eye field, the parietal eye field, the middle superior temporal area, and the principal sulcus region.
Monkeys with unilateral principal sulcus (PS) lesions show a contralateral deficit in localizing remembered targets, especially as the recall interval is lengthened.
An examination of cortex of area 46 in the floor of the principal sulcus in the frontal lobe of the rhesus monkey has been carried out using three young (4-6 years of age), one middle-aged (12 years of age), and five old (25-32 years of age) rhesus monkeys.
The results showed that in comparison to the CONT group, working memory performance significantly enhanced LCGU by 19% in the principal sulcus region of prefrontal cortex and by 11-20% in regions of the inferior parietal cortex corresponding to areas 7A, 7B, 7IP, and 7M. In contrast, LCGU in the principal sulcus was positively correlated with task difficulty. These findings suggest that the enhancement of LCGU in the principal sulcus was primarily influenced by the mnemonic components of the tasks whereas LCGU in the inferior parietal cortex was influenced by their sensory-motor demands.
Then, in the same animal, we placed multiple injections of another retrograde tracer in and around the principal sulcus (Walker's area 46).
We have therefore studied the pattern of intrinsic intra- and interlaminar pyramidal neuron connectivity in prefrontal areas 9 and 46 (of Walker) in macaque monkey cerebral cortex (anterior to the arcuate sulcus between the principal sulcus and midline).
After a few weeks of training, a surface-negative, depth-positive (s-N, d-P) potential (no-go potential) emerged in the dorsal bank of the principal sulcus.
Projections from the FEF terminated in five frontal regions: 1) area FD on the dorsomedial convexity; 2) area FC (containing SEF) medial to the upper limb of the arcuate sulcus; 3) areas FD and FD delta along the walls of the principal sulcus; 4) area FCBm on the deep, posterior wall of the arcuate sulcus inferior to the sulcal spur; and 5) the inferolateral cortex (area FDi) on the convexity and lateral two thirds of the anterior wall of the arcuate sulcus. Projections in sFEF cases tended to be confined to medial parts of dorsomedial FD and FC and the lateral wall of the principal sulcus and inferolateral convexity.
Four rhesus monkeys received unilateral or serial prefrontal lesions in and around the principal sulcus after they reached criterion performance on the ODR tasks.
SEMs were elicited from a small portion of the arcuate fundus and neighboring posterior bank lying directly posterior to the principal sulcus.
On average somatosensory and motor neurons were located more ventrally than the remaining ones, and were concentrated to the middle third of the inferior bank of principal sulcus and adjacent inferior convexity, where a number of somatosensory projections overlap. Oculomotor neurons were found caudally in both banks of principal sulcus and in a narrow band on the dorsal convexity, coinciding with the projection fields of areas 7a and 7ip of posterior parietal cortex, superior colliculus, and paramedian pontine tegmentum.
The area chosen for study is located between the cingulate gyrus and the ventral bank of the principal sulcus, and contains areas 9 and 46 as described by Walker (J.
This approach supports suggestions that the system is divided into a dorsal 'stream' and a ventral 'stream' with limited cross-talk, that these two streams reconverge in the region of the principal sulcus (area 46) and in the superior temporal polysensory areas, that the system is hierarchically organized, and that the majority of the connections are from 'nearest-neighbour' and 'next-door-but-one' areas..
Electron microscopy and immunocytochemistry with a monoclonal antibody against parvalbumin (PV) were combined to analyze the distribution and morphology of PV-immunoreactive (PV-IR) neurons and the synaptology of PV-IR processes in the principal sulcus of the macaque prefrontal cortex. Parvalbumin-IR neurons are present in layers II-VI of the macaque principal sulcus (Walker's area 46) and are concentrated in a band centered around layer IV. PV-IR axons were occasionally observed in the white matter underlying the principal sulcus.
The prefrontal regions above and below the principal sulcus project mainly to the intermediate sector of the head and body of the nucleus.
Injections of WGA-HRP and tritiated amino acids were made in topographically matched regions of the principal sulcus (PS) or of the supplementary motor area (SMA) in each hemisphere, such that the projections from the same area on each side were differentially labeled in the same animal.
Injections of WGA-HRP and tritiated amino acids were made in topographically matched regions of the principal sulcus (PS) or the supplementary motor area (SMA) in each hemisphere, such that the projections from the same area on each side were differentially labeled in the same animal.
In the prefrontal-STs projections, main features of topographic correlation were revealed; the posterior part of the STs area receives fibers from the superior frontal convexity (areas dorsal to the principal sulcus) and areas 8 and 6, whereas the anterior part of the STs area receives fibers from the inferior frontal convexity (areas ventral to the principal sulcus) and the frontal pole (area FD). The principal sulcus sends fibers to the entire STs area except for its ventral wall of the posterior part.
Although the frontal cortex of the baboon brain exhibits the same basic cytoarchitectural features as the frontal corticies of the cercopithecus (campbelli?) (Vogt and Vogt, '19) or the macaque (Walker, '40; Barbas and Pandya, '87, '89), the baboon frontal cortex is very different from that of the macaque and cercopithecus in terms of cytoarchitecture: (1) the baboon frontal cortex has an additional area, termed here "6a gamma", within area 6, which has cytoarchitectural characteristics that are intermediate between those of areas 6 and 8; (2) the aggregation of giant pyramidal cells (greater than 50 microns in diameter) is found only in area 4a in the baboon, whereas such aggregates are found in areas 4a and 4b and, occasionally, in area 4c in the macaque; and (3) area 46 of the prefrontal cortex of the baboon can be subdivided into the cortex that surrounds the principal sulcus (area 46) and the upper and lower banks of the principal sulcus (area 46ps).
In particular, Galago lacks cortex resembling the distinctive, lightly myelinated cortex of the Macaca principal sulcus (Walker's area 46 and its subdivisions).
We conclude that the arcuate areas are common elements of primate GFC organization, while the areas located within and adjacent to the principal sulcus are anthropoid specializations..
Among 434 neurons recorded from prefrontal cortex within and surrounding the principal sulcus (PS), 147 changed their discharge rates in relation to saccadic eye movements in the ODR task.
In the cortex of the dorsal bank of the principal sulcus, surface-negative, depth-positive (s-N, d-P) potentials were recorded specifically on the no-go trial. In the same monkey, the potentials related to the no-go reaction on the auditory stimulus were recorded in the rostral part of the dorsal bank of the principal sulcus, whereas the s-N, d-P potentials on the no-go visual stimulus were observed in the caudal part of the same bank. It is suggested that the dorsal bank of the principal sulcus is essentially related to the integrative functions such as judgement not to move and suppression of motor execution, and that different loci in this cortical area are respectively active for the functions of different sensory modalities..
The discontinuous areas labeled by many different injections included the principal sulcus/frontal eye field region, the anterior cingulate cortex, and the superior temporal polysensory area.
Among 434 neurons recorded from the prefrontal cortex within and surrounding the principal sulcus (PS), 261 had task-related activity during at least one phase of the ODR task, and 74 of these had phasic visual responses to the onset of the visual cues with a median latency of 116 ms.
Injections of HRP were made into area 7 of the parietal lobe or into area 46 in the walls of the principal sulcus. Area 7b, PF, is connected in a well organized and somatotopic manner with the lower premotor area and with the lower part of area 46, below the fundus of the principal sulcus. Area 7a, PG, is connected with area 8a and with the upper part of area 46, above the fundus of the principal sulcus; it is suggested that the lower part of area 8a and the posterior part of area 46 are related to the central visual field, while the medial part of area 8a and the anterior part of area 46 are related to the periphery of the visual field.
Unit activities of the principal sulcus area were recorded in three monkeys (Macaca mullata).
Within the prefrontal cortex, area 7m's connections are with the rostral sector of the frontal eye field (FEF), the dorsal bank of the principal sulcus, and the anterior bank of the inferior arcuate sulcus (Walker's area 45). In contrast, area 7a, on the posterior parietal convexity, is not linked with premotor regions but is heavily interconnected with the rostral FEF in the anterior bank of the superior arcuate sulcus, the dorsolateral prefrontal convexity, the rostral orbitofrontal cortex, area 45, and the fundus and adjacent cortex of the dorsal and ventral banks of the principal sulcus. Area 7b, in the anterior part of the posterior parietal lobule, is interconnected with still a different set of frontal areas, which include the ventral premotor cortex and supplementary motor area, area 45, and the external part of the ventral bank of the principal sulcus. These findings provide a basis for a parcellation of the classically considered association cortex of the frontal lobe, particularly the cortex of the principal sulcus, into sectors defined by their specific connections with the posterior parietal subdivisions.
surface-negative, depth-positive deflexions in the cortex of the dorsal bank of the principal sulcus and of the rostroventral corner of the prefrontal region.
We recorded from 257 neurons in the banks of the posterior third of the principal sulcus of two rhesus monkeys trained to look at a fixation point and make saccades to stimuli in the visual periphery.
Each injection of frontal cortex which labeled the perisylvian somatic cortex involved the cortex of the ventral rim of the principal sulcus (PSvr). This myeloarchitectonic area, which we term area 46vr, is more heavily myelinated than the ventral bank and fundus of the principal sulcus (area 46v) but is less heavily myelinated than the ventral (inferior) convexity (area 12).
Recordings were obtained from 288 neurons in the prefrontal cortex within and surrounding the principal sulcus (PS) while monkeys performed this task.
In each of three experiments with Cynomolgus monkeys (Macaca fascicularis), there was a group of normal control animals, a group with bilateral cortical ablations in the principal sulcus, and a group with fornix transection.
Unilateral arcuate, posterior parietal, or principal sulcus lesions were performed at criterion.
Within 5 min of an injection into one of 7 different sites in the PFC, three different kinds of performance deficit were observed: 1) an increase in the frequency of error responses during the go period in both left-cue and right-cue trials, after injection into the dorso-caudal portion of the principal sulcus (2 sites); 2) an increase in the frequency of directional error responses during the go period in either left-cue or right-cue trials, after injection into the bottom of the middle principal sulcus (3 sites), and 3) an increase in the frequency of omission of responses during the go period, after injection into the dorsal region of the caudal principal sulcus (2 sites). Injections at the remaining 13 sites did not induce any deficits, although injections into the dorsal bank of the principal sulcus (3 sites) induced a decrease in the frequency of the task trials as a result of prolonged intertrial intervals (ITIs).
In certain common target areas, as for example the cingulate cortices, frontal and parietal efferents terminate in an array of interdigitating columns, an arrangement much like that observed for callosal and associational projections to the principal sulcus (Goldman-Rakic and Schwartz, 1982).
In area 46 of the banks of the principal sulcus in the prefrontal cortex, labeled terminals were distributed in all cortical layers or over the entire cortical depth with a lower concentration in layer IV; labeled cells were found mostly in layers III and V, with a relatively high density in layer V..
The tangential distribution of GABA-containing cells was examined in the principal sulcus of the frontal lobe in 12 macaque monkeys. The half-cycle of the low-frequency component (roughly 625 micron) is very similar to the dimensions of afferent and efferent columns in the principal sulcus, while the half-cycle of the higher-frequency component (approximately 125 micron) is closer in size to that of the functionally defined columns of neurons found in regions of sensory cortex that share common physiological properties.
For example, in the lightly innervated fundus of the principal sulcus (area 46), labeled fibers were primarily present in layer I and layers V-VI, whereas in area 9, the most densely innervated region, TH-labeled fibers were present in all cortical layers.
This paper reviews studies on that portion of the prefrontal cortex that is buried in and around the principal sulcus of macaque monkeys and corresponds to Brodmann's area 46 in man. Neuropsychological research as well as neurophysiology and 2-deoxyglucose metabolic mapping indicate that the principal sulcus is essential for regulation of motor behavior by internalized representations of visuo-spatial events. Research over the past decade suggests that the principal sulcus accomplishes its regulatory functions by its interconnections with (1) the posterior parietal cortex which provides it with access to visuo-spatial data, (2) the parahippocampal gyrus and subiculum which allows information to be held 'on line' and deposited in long-term storage, and (3) motor centers such as the basal ganglia, deep layers of the superior colliculus and several premotor areas that control head, eye and hand movements.
Thus circuitry includes connections of the principal sulcus with other areas of parietal association and limbic cortex and projections to the caudate nucleus, superior colliculus, and other premotor centers. Electromicroscopic studies of the principal sulcus and other areas of cerebral cortex show that the number and density of synapses in the cortex increase rapidly, reaching and maintaining higher than normal adult values between 2 and 4 months postnatally, before slowly declining over a period of years to stable adult levels. The capacity to perform delayed-response and/or AB at short delays emerges around 4 months of age, coinciding with the end of the period of highest synaptic density in the principal sulcus.
However, recent anatomical studies have elucidated the circuit basis for motor regulatory functions of the principal sulcus (Brodmann's area 9; Walker's area 46). Recent behavioural and electrophysiological studies in monkeys (Macaca mulatta) demonstrate that the principal sulcus can influence delayed-responding, whether the response is a hand or an eye movement.
Extracellular microelectrode recordings were made in the periarcuate region and dorsal and ventral prefrontal areas near the principal sulcus.
These areas that form a broad ring around the central sulcus are the ventral bank of the principal sulcus and the adjacent area 46, the precentral operculum (PrOC), area SII (Jones and Burton: J.
Single units in the principal sulcus, arcuate area and the inferior convexity of the prefrontal cortex were studied during this task.
There was a topographical relationship between the prefrontal regions containing the majority of labeled cells and the injection sites in the head of the caudate nucleus: the medial orbitofrontal cortex and the medial surface extending downward from the rostral sulcus project ipsilaterally to the medialmost portion of the ventromedial part of the head of the nucleus, the lateral orbitofrontal cortex projects to the ventromedial part of the head of the nucleus, and the dorsolateral prefrontal cortex ventral to the principal sulcus projects to the central part of the head of the nucleus.
The caudal part of the dorsal bank of the principal sulcus was found to be activated specifically on no-go trials during discrimination, and revealed a relatively sharp surface-negative, depth-positive potential. It is suggested that the activity in the dorsal bank of the principal sulcus is related to the judgement not to execute the movement and/or the suppression of motor execution..
Analysis of the thalamus in cases with fluorescent dye injections into the lateral orbital gyrus (Walker's area 11), principal sulcus (area 46), anterior bank of the arcuate gyrus (areas 8 and 45), supplementary motor area (area 6), and motor cortex (area 4) revealed topographic organization of the nigrothalamocortical projection system. The parts of the VAmc and MDmc which receive afferents from the medial part of the SN in turn project to the most anterior regions of the frontal lobe including principal sulcus and orbital cortex. The lateral posterior VAmc, MDmf, MDpc, and MDdc, all of which receive afferents from the lateral part of the SN; project to more posterior regions of the frontal lobe including, in addition to the principal sulcus, the frontal eye field and also areas of the premotor cortex.
Most of the reward-related neurons were located around the rostral end of the principal sulcus.
Horseradish peroxidase (HRP) histochemistry and double labeling with the fluorescent dyes nuclear yellow (NY) and fast blue (FB) were used to examine and compare the laminar and tangential arrangement of ipsilateral (associational) and contralateral (callosal) neurons and their relative density in three regions of prefrontal granular cortex: Walker's area 46 (principal sulcus), area 8A (superior limb of the arcuate sulcus), and area 11 (lateral orbital sulcus). In all three prefrontal regions, neurons with ipsilateral projections were labeled following injections of tracers into the intraparietal sulcus (IPS) and neurons with callosal projections were sequentially or simultaneously labeled with injections into the contralateral principal sulcus (PS).
Extracellular recordings were obtained from 192 neurons located in and around the principal sulcus of the frontal lobe during performance of both control and delay tasks.
Then, the neurons located between the caudal end of the principal sulcus and the arcuate sulcus had RFs with a considerable eccentricity.
Horseradish peroxidase (HRP) gel implants in the prearcuate frontal cortex dorsal to the caudal third of the principal sulcus in the monkey resulted in an anterogradely labeled bilateral projection to this paraoculomotor cell group.
None of these nuclei contained labeled neurons following HRP injections into the principal sulcus or the lateral inferior convexity of the frontal lobe.
Monkeys with ablations of the cortex in the principal sulcus who were impaired on a spatial delayed reaction test were unimpaired on a time discrimination test in which length of time since the last trial signalled the spatial position of the correct foodwell.
A unilateral lesion of the principal sulcus did not cause symptoms of neglect in the visual-motor guidance task.
Following injections of HRP into the dorsal portion of the post-arcuate area, retrogradely labeled cells appeared in the arcuate area dorsal to the principal sulcus, while, following injections into its ventral portion, labeled cells appeared in the arcuate area ventral to the principal sulcus.
Two brain regions implicated for their role in age-related cognitive disturbances, the hippocampus and the gyri bordering the principal sulcus in the frontal cortex were selected for these comparisons.
In order to assess the roles of the posterior parieto-occipital and principal sulcus cortices in processing spatial information, both with and without delays, monkeys were given lesions of one or the other area or no lesion and tested on a series of conditional discrimination tasks. The animals with the principal sulcus removed appeared to have difficulty only when they were required to respond with reference to the colors of the response alternatives. This suggests that these animals had a tendency to respond without reference to the color dimension, but rather just to the presentation of the response array, and therefore a principal sulcus function of inhibiting a response until the appropriate information has been processed..
Although the functional significance of the midprincipalis region is well known, the afferent and efferent connections of this zone, in comparison to the anterior and posterior portions of the cortex lining the principal sulcus, are poorly understood. In 3 animals the retrograde tracer HRP and the anterograde tracers, tritiated proline, lysine and leucine, were injected into the sulcal cortex lining the principal sulcus. The cortex forming the banks of the principal sulcus was divided into anterior, middle and posterior sectors with one animal used for each zone. As expected from previous studies, the heaviest afferents to the cortex forming the principal sulcus were from the parvocellular portions of the medical dorsal nucleus. The medial pulvinar nucleus and the nucleus limitans projected to only the anterior and posterior portions of the cortex lining the principal sulcus. Although cells were seen in the hypothalamus following injections in all 3 sectors of the cortex lining the principal sulcus, the heaviest hypothalamic projections were noted after injections into the mid-sector of the cortex.
Separate groups of monkeys were trained on delayed object alternation, delayed object matching, and delayed color matching, after which half the animals in each group received lesions of the cortex in the principal sulcus, and the other half, lesions of the inferior frontal convexity. By contrast, the principal sulcus lesions, which yield such severe deficits on spatial memory tasks, led to only small, transient disruptions on each of the three non-spatial tasks. According to these results, the non-spatial memory deficits that have been found after unrestricted lateral prefrontal lesions are due mainly to damage below the principal sulcus in the inferior prefrontal cortex. The function of the tissue in the principal sulcus itself, on the other hand, appears so far to be limited largely to the spatial modality..
Such processes as combining the external stimuli into the integrated program, preservation of short term memory traces, correct and incorrect experimental task solution are reflected in principal sulcus neuronal activity.
The terminal distribution of cortico-cortical connections was examined by autoradiography 7-8 days following injections of tritium labeled amino acids into the dorsal bank of the principal sulcus, the posterior part of the medial orbital gyrus, or the hand and arm area of the primary motor cortex in monkeys ranging in age from 4 days to 5.5 months.
The distribution of prefronto-caudate fibers in the caudate nucleus was studied autoradiographically in monkeys of various ages in which tritiated amino acids had been injected into the middle one-third of the length of the dorsal bank of the principal sulcus.
The frontal lobe connections of the post-Rolandic sensory association areas are investigated; Our results indicate that the caudal portion of the superior temporal gyrus (area 22), the lateral peristriate belt (area 18,19), and the superior parietal lobule and the rostralmost portion of the inferior parietal lobule (areas 5 and 7), all project to periarcuate cortex, while the middle portion of area 22, caudal infero-temporal cortex (area 20), and the middle portion of the lower bank of the intraparietal sulcus, all have connections predominantly to prearcurate cortexmin contrast, rostral area 22 and the rostral inferotemporal cortex (area 21) project primarily to the orbital surface, and the middle portion of area 7 projects to the mid-principal sulcus. Those regions that project to periarcuate cortex are termed first association areas (AA1, VA1, SA1), those that project primarily to prearcuate cortex are designated second association areas (AA2, VA2, SA2), while those that project mainly to the orbital surface or the mid-principal sulcus are called third association areas (AA3, VA3, SA3).
Monkeys had nonpolarizable electrodes implanted bilaterally in prefrontal (principal sulcus), precentral, and occipital cortex.
Monkeys with bilateral lesions of the anterior, miiddle, or posterior thirds of the principal sulcus, of the periarcuate prefrontal region, or of the inferior parietal lobule were tested for retention of spatial delayed-alternation.
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