Short-latency preference for faces in the primate superior colliculus

Face processing is fundamental to primates and has been extensively studied in higher-order visual cortex. Here we report that visual neurons in the midbrain superior colliculus (SC) display a preference for faces, that the preference emerges within 50ms of stimulus onset - well before "face patches" in visual cortex - and that this activity can distinguish faces from other visual objects with accuracies of ~80%. This short-latency preference in SC depends on signals routed through early visual cortex, because inactivating the lateral geniculate nucleus, the key relay from retina to cortex, virtually eliminates visual responses in SC, including face-related activity. These results reveal an unexpected circuit in the primate visual system for rapidly detecting faces in the periphery, complementing the higher-order areas needed for recognizing individual faces.

Correlated variability in primate superior colliculus depends on functional class

Correlated variability in neuronal activity (spike count correlations, r_SC) can constrain how information is read out from populations of neurons. Traditionally, r_SC is reported as a single value summarizing a brain area. However, single values, like summary statistics, stand to obscure underlying features of the constituent elements. We predict that in brain areas containing distinct neuronal subpopulations, different subpopulations will exhibit distinct levels of r_SC that are not captured by the population r_SC. We tested this idea in macaque superior colliculus (SC), a structure containing several functional classes (i.e., subpopulations) of neurons. We found that during saccade tasks, different functional classes exhibited differing degrees of r_SC. "Delay class" neurons displayed the highest r_SC, especially during saccades that relied on working memory. Such dependence of r_SC on functional class and cognitive demand underscores the importance of taking functional subpopulations into account when attempting to model or infer population coding principles.

Temporal integration is a robust feature of perceptual decisions

Making informed decisions in noisy environments requires integrating sensory information over time. However, recent work has suggested that it may be difficult to determine whether an animal's decision-making strategy relies on evidence integration or not. In particular, strategies based on extrema-detection or random snapshots of the evidence stream may be difficult or even impossible to distinguish from classic evidence integration. Moreover, such non-integration strategies might be surprisingly common in experiments that aimed to study decisions based on integration. To determine whether temporal integration is central to perceptual decision making, we developed a new model-based approach for comparing temporal integration against alternative 'non-integration' strategies for tasks in which the sensory signal is composed of discrete stimulus samples. We applied these methods to behavioral data from monkeys, rats, and humans performing a variety of sensory decision-making tasks. In all species and tasks, we found converging evidence in favor of temporal integration. First, in all observers across studies, the integration model better accounted for standard behavioral statistics such as psychometric curves and psychophysical kernels. Second, we found that sensory samples with large evidence do not contribute disproportionately to subject choices, as predicted by an extrema-detection strategy. Finally, we provide a direct confirmation of temporal integration by showing that the sum of both early and late evidence contributed to observer decisions. Overall, our results provide experimental evidence suggesting that temporal integration is an ubiquitous feature in mammalian perceptual decision-making. Our study also highlights the benefits of using experimental paradigms where the temporal stream of sensory evidence is controlled explicitly by the experimenter, and known precisely by the analyst, to characterize the temporal properties of the decision process.

What is attention?

We define attention as "the set of evolved brain processes that leads to adaptive and effective behavioral selection." Our emphasis is on understanding the biological and neural mechanisms that make the behavioral properties of attention possible. Although much has been learned about the functional operation of attention by postulating and testing different aspects of attention, our view is that the distinctions most frequently relied upon are much less useful for identifying the detailed biological mechanisms and brain circuits. Instead, we adopt an evolutionary perspective that, while speculative, generates a different set of guiding principles for understanding the form and function of attention. We then provide a thought experiment, introducing a device that we intend to serve as an intuition pump for thinking about how the brain processes for attention might be organized, and that illustrates the features of the biological processes that might ultimately answer the question. This article is categorized under: Cognitive Biology > Evolutionary Roots of Cognition Psychology > Attention Philosophy > Psychological Capacities.

Microsaccades as a marker not a cause for attention-related modulation

Recent evidence suggests that microsaccades are causally linked to the attention-related modulation of neurons—specifically, that microsaccades toward the attended location are required for the subsequent changes in firing rate. These findings have raised questions about whether attention-related modulation is due to different states of attention as traditionally assumed or might instead be a secondary effect of microsaccades. Here, in two rhesus macaques, we tested the relationship between microsaccades and attention-related modulation in the superior colliculus (SC), a brain structure crucial for allocating attention. We found that attention-related modulation emerged even in the absence of microsaccades, was already present prior to microsaccades toward the cued stimulus, and persisted through the suppression of activity that accompanied all microsaccades. Nonetheless, consistent with previous findings, we also found significant attention-related modulation when microsaccades were directed toward, rather than away from, the cued location. Thus, despite the clear links between microsaccades and attention, microsaccades are not necessary for attention-related modulation, at least not in the SC. They do, however, provide an additional marker for the state of attention, especially at times when attention is shifting from one location to another.

Midbrain activity shapes high-level visual properties in the primate temporal cortex

Recent fMRI experiments identified an attention-related region in the macaque temporal cortex, here called the floor of the superior temporal sulcus (fSTS), as the primary cortical target of superior colliculus (SC) activity. However, it remains unclear which aspects of attention are processed by fSTS neurons and how or why these might depend on SC activity. Here, we show that SC inactivation decreases attentional modulations in fSTS neurons by increasing their activity for ignored stimuli in addition to decreasing their activity for attended stimuli. Neurons in the fSTS also exhibit event-related activity during attention tasks linked to detection performance, and this link is eliminated during SC inactivation. Finally, fSTS neurons respond selectively to particular visual objects, and this selectivity is reduced markedly during SC inactivation. These diverse, high-level properties of fSTS neurons all involve visual signals that carry behavioral relevance. Their dependence on SC activity could reflect a circuit that prioritizes cortical processing of events detected subcortically.

A simple linear readout of MT supports motion direction-discrimination performance

Motion discrimination is a well-established model system for investigating how sensory signals are used to form perceptual decisions. Classic studies relating single-neuron activity in the middle temporal area (MT) to perceptual decisions have suggested that a simple linear readout could underlie motion discrimination behavior. A theoretically optimal readout, in contrast, would take into account the correlations between neurons and the sensitivity of individual neurons at each time point. However, it remains unknown how sophisticated the readout needs to be to support actual motion-discrimination behavior or to approach optimal performance. In this study, we evaluated the performance of various neurally plausible decoders, trained to discriminate motion direction from small ensembles of simultaneously recorded MT neurons. We found that decoding the stimulus without knowledge of the interneuronal correlations was sufficient to match an optimal (correlation aware) decoder. Additionally, a decoder could match the psychophysical performance of the animals with flat integration of up to half the stimulus and inherited temporal dynamics from the time-varying MT responses. These results demonstrate that simple, linear decoders operating on small ensembles of neurons can match both psychophysical performance and optimal sensitivity without taking correlations into account and that such simple read-out mechanisms can exhibit complex temporal properties inherited from the sensory dynamics themselves.NEW & NOTEWORTHY Motion perception depends on the ability to decode the activity of neurons in the middle temporal area. Theoretically optimal decoding requires knowledge of the sensitivity of neurons and interneuronal correlations. We report that a simple correlation-blind decoder performs as well as the optimal decoder for coarse motion discrimination. Additionally, the decoder could match the psychophysical performance with moderate temporal integration and dynamics inherited from sensory responses.

Publisher Correction: Midbrain activity can explain perceptual decisions during an attention task

The original and corrected figures are shown in the accompanying Publisher Correction.

Midbrain activity can explain perceptual decisions during an attention task

We introduce a decision model that interprets the relative levels of moment-by-moment spiking activity from the right and left superior colliculus to distinguish relevant from irrelevant stimulus events. The model explains detection performance in a covert attention task, both in intact animals and when performance is perturbed by causal manipulations. This provides a specific example of how midbrain activity could support perceptual judgments during attention tasks.

The Role of the Lateral Intraparietal Area in (the Study of) Decision Making

Over the past two decades, neurophysiological responses in the lateral intraparietal area (LIP) have received extensive study for insight into decision making. In a parallel manner, inferred cognitive processes have enriched interpretations of LIP activity. Because of this bidirectional interplay between physiology and cognition, LIP has served as fertile ground for developing quantitative models that link neural activity with decision making. These models stand as some of the most important frameworks for linking brain and mind, and they are now mature enough to be evaluated in finer detail and integrated with other lines of investigation of LIP function. Here, we focus on the relationship between LIP responses and known sensory and motor events in perceptual decision-making tasks, as assessed by correlative and causal methods. The resulting sensorimotor-focused approach offers an account of LIP activity as a multiplexed amalgam of sensory, cognitive, and motor-related activity, with a complex and often indirect relationship to decision processes. Our data-driven focus on multiplexing (and de-multiplexing) of various response components can complement decision-focused models and provides more detailed insight into how neural signals might relate to cognitive processes such as decision making.

Differential effects of deep TMS of the prefrontal cortex on apathy and depression

BACKGROUND

Apathy is one hallmark of major depression (MDD). It is distinguished by lack of emotion, whereas other aspects of depression involve considerable emotional distress. Investigating both apathy and depression may increase the degree of treatment efficacy for both ailments together and apart.

OBJECTIVE

Evaluate the differential effects of deep transcranial magnetic stimulation (DTMS) over the prefrontal cortex (PFC) on apathy and other aspects of depression in patients suffering from a depressive episode.

METHODS

Fifty-four treatment-resistant MDD patients were evaluated with the Hamilton Rating Scale for Depression (HRSD), and then treated with DTMS. Apathy-related items from HRSD (ApHRSD) were compared with the remaining items from HRSD (DepHRSD). Antidepressant medications were withdrawn and active DTMS treatment was administered at 20 Hz, 5 days a week for 4 weeks. Changes in HRSD were recorded. Primary efficacy time point was 1 week after the end of active treatment.

RESULTS

At screening, ApHRSD distribution was unimodal (moderate apathy), with low correlation (r = 0.17) between ApHRSD and DepHRSD. After treatment, a third had remitted apathy, and the correlation between ApHRSD and DepHRSD had dramatically increased (r = 0.83). Severe ApHRSD (≥ 7) at screening correlated with nonremission for both ApHRSD (R(2) = 0.1993, P = .0012) and DepHRSD (R(2) = 0.0860, P = .0334).

CONCLUSIONS

DTMS over the PFC improved both apathy and depression similarly. However, DTMS did not lead to MDD remission if ApHRSD at screening was ≥ 7 of 12. Further investigation using a larger sample will determine whether screening apathy at baseline could be used to predict efficacy of DTMS in MDD patients.

RENAL INSUFFICIENCY FOLLOWING TRYPSIN INJECTION INTO THE RENAL ARTERIES

1. The injection of trypsin into both renal arteries of the dog was found to cause an acute necrosis of large sections of the kidney, an immediate excretory insufficiency, and a transient hypertension. 2. Dogs surviving the acute phase of the trypsin injection, developed a chronic renal excretory insufficiency with no hypertension, despite the severity and duration of the renal excretory insufficiency. 3. The application of a Goldblatt clamp to the renal artery of one of the two kidneys, previously injected with trypsin, led to a rise in blood pressure which returned at once to normal when the ischemic kidney was removed, even though the pre-existing renal excretory insufficiency was augmented. This experience demonstrated unequivocally that chronic renal excretory insufficiency and hypertension are not directly related. 4. The application of a Goldblatt clamp to the renal artery of one kidney and the simultaneous injection of trypsin into the other led to a hypertension. The later removal of the ischemic kidney led to a severe renal excretory insufficiency, at the same time the pre-existing hypertension disappeared. This indicated again that renal excretory insufficiency and renal ischemia produced different phenomena and that the former had no direct relation to hypertension.

THE ROLE OF RENAL METABOLISM IN HYPERTENSION AND UREMIA

1. The chemical mediator of renal hypertension is rapidly destroyed by the metabolic activity of the normal kidney. The excretory function of the kidney plays little, if any, rôle in eliminating the mediator of hypertension. 2. If specific substances are responsible for the uremic syndrome, they are neither produced nor eliminated to any significant extent by the metabolic activity of the kidneys. The elimination of these postulated uremia-producing substances would have to be primarily dependent upon the excretory activities of the kidney. 3. No evidence was obtained to support the view that a unilateral ureterovenous fistula leads to "nephrotoxic" symptoms.

[Various data concerning the ultrastructure of Proteus spheroplasts]

Spheroplasts were obtained under the action of penicillin on the same medium which was later used to obtain the L-forms. Spheroplast formation started 15 to 20 minutes after the addition of penicillin and reached the maximum in 2 hours. The first dividing forms were revealed at that time, and this division continued for at least 24 hours. The majority of the cells represented spheroplasts surrounded by outer and cytoplasmic membrane, and only some--true protoplasts--had cytoplasmic membrane alone. Division was anomalous in comparison with the bacterial forms with the cell wall: it was noted that either both daughter cells were surrounded by a common outer membrane, or one daughter cell had two membranes serving as a spheroplast and the other--one membrane, serving as a true protoplast. Individual vesicles and myelin-like structures were found to be extruded into the periplasmic space or directly into the surrounding environment. In the latter case pearl-like structures described by Ryter in the formation of protoplasts in bacilli were observed. However, in the Proteus such structures were largely formed by the material of the plastic layer of the cell wall, and to a lesser extent--by the lipoproteid membrane.

Physical fitness and coronary heart disease. Some basic views

The purposes of a physical training program are examined and the evidence for the general and circulatory benefits of physical fitness is discussed. While the proof of benefits is not established, there is sufficient evidence from current studies to justify encouragement of the exercise programs. The evidence that exercise lessens experimental atherogenesis is equivocal. The possibility that physical fitness alters the morbidity and mortality of coronary sclerosis remains conjectural. Whether a physical fitness program would (1) lessen the incidence of intravascular thrombosis or atheromatous ulceration, (2) increase the extent or rate of development of coronary collaterals in man although the evidence in animals is suggestive, (3) improve the performance capacity of the heart, (4) decrease the likelihood of arrhythmias, or (5) result in more efficient bodily responses to the stresses associated with myocardial infarction is not clear or has not been definitely ascertained because of lack of evidence.

Counterpulsation effects of coronary blood flow and cardiac oxygen utilization

Counterpulsation in dogs with normal systemic arterial blood pressure produced a reduction in myocardial oxygen consumption without a significant concomitant change in total coronary flow. In dogs with a deteriorating heart and low systemic arterial blood pressure, myocardial oxygen consumption became dependent on coronary flow. Under these circumstances, counterpulsation produced an increase in coronary flow, and with it a secondary augmentation of cardiac oxygen consumption. Counterpulsation reduced the mean systemic arterial blood pressure during ventricular ejection to a greater degree when the control level of this pressure was normal than when it was hypotensive. This lessened effect may also occur when the heart has deteriorated. The mechanisms involved in causing the several effects of counterpulsation are discussed.

Effect of estrogen dosage upon plasma, liver and bile lipids in cholesterol-fed cockerels

The effects of four dosages of conjugated equine estrogens (Premarin) on atherogenesis and on plasma, liver and bile lipids were studied in cockerels maintained on a high-fat, high-cholesterol diet. A lowering effect, not dose-dependent, occurred in plasma linoleic and linolenic acid. An augmentative effect, varying with dose, occurred in plasma phospholipids, plasma palmitic, stearic and oleic acids, liver total fat and thoracic atherosclerosis. A lowering, dose-dependent effect occurred in coronary atherosclerosis, plasma cholesterol-phospholipid ratio and plasma arachidic acid. A diphasic, dose-dependent, response occurred in: (1) plasma cholesterol (decrease at lowest dosage and increase at higher dosages); (2) bile cholesterol (increase at lower dosages and a decrease at higher dosages); (3) liver cholesterol (increase at lowest dose, and decrease at higher dosages); (4) plasma arachidonic acid (increase at lower and decrease at higher dosages). The mechanisms responsible for these changes are not clear but are under investigation.

Failure of D- and L-thyroxine to protect cholesterol and oil fed cockerels against coronary atherogenesis

In cockerels, L-thyroxine was significantly more active biologically than an equivalent dose of D-thyroxine, or even four times the dose, as demonstrated by the effects on body weights, organ weights and comb index.

In cockerels fed an atherogenic diet, the plasma cholesterol concentrations in all the thyroxine-treated groups were significantly lower than in the control groups.

No consistent effect of D-thyroxine on thoracic aorta atherosclerosis was observed. However, L-thyroxine had some protective action in the one experiment done.

Despite suppression of hypercholester-olemia, no protection against coronary atherosclerosis was seen with the administration of either L- or D-thyroxine. In fact, with an increase in dose of D-thyroxine to 4 mg, there developed actually an increase in the percentage of coronary vessels showing atherosclerosis.

These observations confirm once again the importance of avoiding reliance exclusively on blood cholesterol levels when judging the effects of hormones on atherogenesis.

Influence of various dietary fats on hypercholesterolemia and atherogenesis in cockerels

When cockerels were given a cholesterol supplemented, fat-free, semi-synthetic diet as the basic ration, all oils and solid fats were atherogenic and caused elevated serum cholesterol levels. The degree of hypercholesterolemia and atherogenesis was related to fatty acid composition of the fat fed. Margarines were less atherogenic and less hypercholesterolemic than oils. The additives used in the preparation of margarine have some influence on maintaining lower cholesterol levels, but do not appear to have any significant effects on atherogenesis. The structural isomers formed during margarine manufacture may be responsible through an alteration of lipid metabolism.

Benefit from testosterone and hydrocortisone on coronary atherogenesis in cockerels on a low protein atherogenic diet

In the presence of high fat and high cholesterol in the diet, growing cockerels showed more marked hypercholesterolemia and atherosclerosis when their protein intake was low. Testosterone counteracted both the increased hypercholesterolemic and the enhanced atherogenic effects of a low protein diet. Hydrocortisone markedly aggravated the hypercholesterolemia in these cockerels but offered significant protection against coronary atherogenesis when associated with a low protein intake. When the dietary protein level is adequate neither testosterone nor hydrocortisone lowered coronary atherogenesis, despite modification of plasma cholesterol levels. Protein level in the diet must be considered in evaluating hormonal atherogenic effects.

Experimental demonstration of concealed AV conduction in the human heart

Artificial pacing of patients with Stokes-Adams disease provided an opportunity to study experimentally the ways of operation of concealed antegrade or retrograde conduction, or both, in the AV junction.

With a catheter electrode in the right atrium the classical experiment of Lewis and Master was repeated, revealing, during a 2:1 ventricular response to an atrial tachycardia, the delaying effect of seemingly blocked atrial impulses on subsequent AV conduction.

Shifting the position of a single premature atrial impulse within a constant driving cycle of the atria produced graded effects of "blocked" atrial impulses on AV junctional refractoriness, permitting an estimation of the duration of the "phase of concealed AV conduction."

Interpolation of such premature atrial impulses into successive driving cycles resulted in "repetitive concealed conduction."

In an artificially produced atrial parasystole there was observed "concealed discharge" of a subsidiary (escaping) AV junctional pacemaker by an apparently nonconducted atrial impulse.

With a catheter electrode in the right ventricle in a case of advanced AV block, concealed retrograde conduction of pacer stimuli disturbed the rhythmicity of a spontaneous AV junctional pacemaker.

In a case of advanced AV block with preserved retrograde conduction (unidirectional block), evidence of penetration of the upper AV junction by the "blocked" antegrade impulse was found.

With electrodes implanted in the left ventricle in a case of advanced AV block, concealed retrograde conduction of the artificial pacemaker stimuli enhanced antegrade conduction by transiently changing an area of unidirectional block to one of supernormal conduction.

Thus, all known manifestations of concealed atrioventricular and ventriculo-atrial conduction, occurring spontaneously in clinical records or induced in animal experiments, were artificially reproduced in the human heart.

THE EFFECT OF HIGH PROTEIN DIETS ON EXPERIMENTAL RENAL HYPERTENSION

The effect of high and low protein diets were studied on fourteen dogs in twenty-four different experiments. In only two of these animals, both with moderate renal excretory failure, was a reversible rise in blood pressure elicited by a high protein diet. The possible mechanisms involved in meeting an increased excretory load are discussed.