Psychology and Neuroscience: Neural Correlates Defined

Psychology and Neuroscience: Neural Correlates Defined

Cogito ergo sum – mathematician Rene Descartes, Latin for “I think therefore I am”

Neurons that fire together, wire together – Donald O. Hebb (on the subject go neuroplaticity)

The Neural Correlates of Memory

Surface electrodes are a noninvasive method to record brain activity. Together with electrophysiology and other techniques, neuroimaging permits to transcribe brain activity. Accordingly, the fusiform gyrus has been documented as critical for processing facial information. Also, cells which are most active during tasks involving face recognition have been dubbed ‘face neurons’. Thus, damage to the area may result in prosopagnosia, or the inability to recognize faces. To clarify the neural correlates of associative memory of familiarity, Eifuku et al. (2010) recorded activity from a macaque’s AITv*. The AITv was found to represent pair-associative learning of facial identity information in the monkey brain. Consequently, a lesion in the region would likely result in the associative subtype of prosopagnosia.

Further, attention has long been established as facilitating retention. Ritchey et al. (2011) attest that neural correlates of memory depend on stages and processes. So, the authors draw on the ‘levels of processing theory’ to verify, using fMRI and depictions of facial expressions, if emotion does indeed facilitate memory storage. For instance, during shallow encoding, the amygdala seems to lead the process; in particular, for negatively tainted content. However, in the deep encoding stage, the PFC is more active; especially, for stimuli with positive valence. Therefore, the experimenters were able to prove their hypothesis that “emotional memory encoding in the shallow condition would be primarily supported by the amygdala, whereas deep emotional memory encoding would additionally benefit from memory-related activity in vlPFC [4 experimental conditions: shallow/deep, positive/negative]” (Ibid, 765).

Where Memory lives. Image: Megan Jorgensen (Elena)

The hippocampus is most associated with memory, perhaps because of the famous patient HM and the London taxi drivers study. As expected, the researchers report hippocampal involvement as superseding both phases. In addition to confirming amygdalar and hippocampal activation during emotional material encoding, Brohawn et al. (2010) show that activation of these regions is greater in patients with PTSD. Moreover, activity levels correlate with symptom severity.

Interestingly, Rabin et al. (2009) point out that AM and ToM (the ability to infer others’ feelings and thoughts) share many of the same circuitry. Namely, hippocampus, parahippocampal cortex, entorhinal/perirhinal cortex, precuneus, paracingulate cortex, frontal poles, VLPFC, DMPFC, posterior cingulate/retrosplenial cortex, MTG, TP, and occipital cortex. The authors similarly outlined the regions stimulated differentially during the two tasks (results omitted in the present short essay). Notwithstanding, their findings may explain why some individuals with brain damage retain their ToM abilities, despite suffering from amnesia.

Our thoughts and our world. Image:Megan Jorgensen

The Neural Correlates of Thought

Understanding neural correlates of thought is further complicated by the subjectivity of the concept’s definition. Nonetheless, it seems reasonable to assume that processes such as conscious experience and verbal insight require some form of thinking. On the one hand, in regards to conscious experience, Stawarczyk and colleagues (2011) support the notion stating that the Default Mode Network (DMN) underlies cognitive processes. In a series of tests, they found activations in the following brain regions: medial prefrontal cortex, posterior cingulate cortex/precuneus, lateral temporal regions and posterior inferior parietal lobe.

On the other hand, Watanabe (2011) wondered if there were internal thinking mechanisms in the monkey. The writer confirms the default system, which asserts that brain activity is highest during attentional rest, and describes it as comprising the medial prefrontal and medial parietal regions. Monkeys seem to possess a similar structural organization. In outlining focal clusters, an important note to keep in mind is how active the whole cerebrum is. After all, phrenology, the obsolete view of extreme modularity, was largely refuted. In other words, the brain seems to be big on team work.

Notwithstanding, in spite of how hard cognitive processes such as thinking are to study due to their subjective properties, neural correlates of thought have still been looked into by researchers such as Zhang et al. (2011). Drawing on Event Related Potentials (ERPs), the authors concentrated on mental prowess needed to solve verbal problems. Thus, the cortical areas activated were, curiously enough, the fusiform gyrus (also associated with face recognition) and the right superior temporal gyrus.

Our thoughts are what we are. Image: Megan Jorgensen (Elena)

Alternatively, Rodriguez-Ferreiro and coauthors turned to abstract (low imageability) Spanish verbs only to stimulate activity in the inferior frontal, anterior temporal, and posterior temporal, areas. The same regions have also previously been linked to semantic retrieval. Although much remains to be done by neuroscientists, the four works discussed above significantly contribute to our understanding of neural correlates of thought and related processes. One may reasonably argue that conscious experience, verbal processing and insight constitute thinking, thus neural substrates of these events shed light on how the brain ‘thinks’.

ABBREVIATIONS:

AITv — Anterior Inferior Temporal (cortex), ventral

AM — Autobiographical Memory

DMPFC — DorsoMedial PreFrontal Cortex

MTG — Middle Temporal Gyrus

PTSD — Post Traumatic Stress Disorder

TP — Temporal Poles

ToM — Theory of Mind

VLPFC — VentroLateral PreFrontal Cortex

Old times and modern thoughts. Image: Megan Jorgensen (Elena)

Glossary

The following are some of the terms often encountered in neuroscientific research. Psychology similarly draws on the database.

ACETYLCHOLINE: A major neurotransmitter in the brain. The enzyme that breaks it down is called acetylcholinesterase.

AMYGDALA: Almond shaped nuclei in the temporal lobe. Part of the limbic system, mediate emotional reactions and memory.

AUTONOMIC NERVOUS SYSTEM (ANS): Divided into the sympathetic and parasympathetic nervous systems. The sympathetic orchestrates the fight-or-flight (or freeze) response, while its parasympathetic counterpart modulates metabolism, thermoregulation and homeostasis maintenance.

BRAIN: The brain is part of the Central Nervous System (CNS) and is divided into two hemispheres and four lobes. The four lobes are: frontal, parietal, temporal and occipital.

BRAINSTEM: The brainstem is the posterior part of the mammalian brain, continuing downwards to join the spinal cord.

BLIND SPOT: The location where the optic nerve leaves the eye lacks photoreceptors (rods and cones). Thus, there is no visual input for that, albeit small, part of the visual field. However, since the brain fills in the missing information from context and information form the other eye, humans are usually unaware of its existence.

GOLGI STAIN: A method developed by Camillo Golgi in 1873, which consists of “staining” neurons with chemicals they react to, making them visible and thus possible to outline projections.

INTERNEURONS: Also called relay neurons, interneurons connect afferent and efferent pathways.

LONELINESS: The psychological definition of loneliness (as defined by psychologists) is not the absence of, but the dissatisfaction with one’s, relationships. In contrast, solitude relates a state of contentment despite aloneness.

MOTOR CORTEX: The part of the brain that is primarily responsible for movement is called the motor cortex. Other, adjacent structures also influencing motion are the premotor and sensorimotor cortices. The localized homunculous is a topographical representation of the human body.

NEUROMARKETING: The application of neuroscientific knowledge to business practices. Often criticized as unethical and immoral.

NEURON: Brain cells consisting of a body (soma) and an elongated portion projecting outwards (axon). Short projections from neurons are called dendrites.

NEUROREGENERATION: Regrowth or repair of nerve or other cell tissue. The process differs between the Central Nervous System (CNS) and Peripheral Nervous System (PNS).

NEUROSCIENCE: The scientific study of the nervous system (brain, spinal cord and peripheral nervous system). Traditionally considered a branch of biology, neuroscience is an interdisciplinary field, combining elements from other disciplines such as computer science, chemistry, mathematics, physics, linguistics, philosophy, psychology, medicine and engineering.

NEUROSTRANSMITTERS: Neurotransmitters are neurochemicals, or chemical messengers in the brain.

OLFACTORY BULB: The olfactory bulb is the forebrain structure primarily associated with the sense of smell.

PSYCHOLOGY: Psychology, especially neuropsychology, is a field close to neuroscience. Psychological disciplines are: experimental, cognitive, social, personality, abnormal, developmental, computational, evolutionary, positive, cultural and biological.

SfN (Society for Neuroscience): Society for Neuroscience is a non-profit membership organization for physicians and scientists studying the nervous system. Headquarters are located in Washington, DC; USA.

STARTLE RESPONSE: Brainstem reflex aimed at protecting the organism and enabling sudden reaction. The behavioural phenomenon is present in many species.

STELLATE NEURONS: Stellate neurons get their name because their shapes resemble those of stars. There are three main types: aspiny stellate cells, inhibitory interneurons and excitatory spiny stellate interneurons.

TALAIRACH COORDINATES: Talairach coordinates map the human brain. MNI (Montreal Neurological Institute) coordinates are additionally used.

THEORY OF MIND (TOM): The ability to infer others’ motivations and beliefs. Largely thought to develop faster in children with siblings and impaired in autism.

UPTAKE PUMP: When neurotransmitter are transported back inside the terminal, the process is accomplished with the uptake pump. For that purpose, neurochemicals such as dopamine, serotonin or acetylcholine bind to this protein.

VALENCE: In neuroscience, the term valence refers to emotional value associated with stimuli. Thus, valence may be positive or negative.

VESICLES: Inside the axon’s terminal, there are small pouches dubbed vesicles. When a neuron fires, they release neurotransmitters into the synaptic cleft.

ZEITGEBER: Synchronization clues from the environment. The word is derived from German, literally meaning ‘time givers’.

ZEITGEIST: Also a German word, meaning the spirit of the time. However, the expression has since come to represent how explanations in the scientific community are influenced by the ideologies of their surroundings.

We are the fruits. Photo : Megan Jorgensen (Elena)

References:

• Brohawn, K. H., Offringa, R., Pfaff, D. L., Highes, K. C. & Shin, L. M. (2010). The neural correlates of emotional memory in posttraumatic stress disorder. Biological Psychiatry, 68: 1023-30.
• Eifuku, S., Nakata,R., Sugimori, M., Ono, T. 2 & Tamura, R. (2010). Neural correlates of associative face memory in the anterior inferior temporal cortex of monkeys. The Journal of Neuroscience, 30 (45): 15085–96.
• Rabin, J. S., Gilboa, A., Stuss, D. T., Mar, R. A. & Rosenbaum, S. R. (2009). Common and unique neural correlates of autobiographical memory and theory of mind. Journal of Cognitive Neuroscience, X (Y): 1-17
• Ritchey, M., LaBar, K. S. & Cabeza, R. (2011). Level of processing modulates the neural correlates of emotional memory formation. Journal of Cognitive Neuroscience, 23 (4): 757-71.
• Rodriguez-Ferreiro, J., Gennari, S. P., Davies, R. & Cuetos, F. (2009). Neural correlates of abstract verb processing. Journal of Cognitive Neuroscience, X (Y): 1-13.
• Stawarczyk, D., Majerus, S., Maquet, P. & D’Argembeau, A. (2011). Neural correlates og ongoing conscious experience: Both task-unrelatednesss and stimulus-independence are related to default network activity. PLoS ONE, 6 (2): e-16997.
• Watanabe, M. (2011). Are there internal thought processes in the monkey? – Default brain activity in humans and nonhuman primates. Behavioural Brain Research, 221: 295-303.
• Zhang, M., Tian, F., Wu, X., Liao, S. & Qui, J. (2011). The neural correlates of insight in Chinese verbal problems: An event related-potential study. Brain Research Bulletin, 84: 210-4.